From ef6a567aba378088fe7402bbeb4f329526e2fe43 Mon Sep 17 00:00:00 2001
From: Edward Xu <edxu96@outlook.com>
Date: Sun, 28 Feb 2021 10:14:10 +0100
Subject: [PATCH] update docs to 0.2.7

---
 docs/_modules/index.html                      |   9 +-
 .../graph/{planar.html => geographic.html}    |  54 +--
 docs/_modules/mgrid/graph/supra.html          |  45 ++-
 .../grid/{planar.html => geographic.html}     |  32 +-
 docs/_modules/mgrid/grid/supra.html           |  20 +-
 .../_modules/mgrid/power_flow/conversion.html |  25 +-
 docs/_modules/mgrid/power_flow/delivery.html  |   3 +-
 .../_modules/mgrid/power_flow/pandapower.html |   5 +-
 docs/_modules/mgrid/power_flow/series.html    | 232 ++++++++++++
 docs/_modules/mgrid/power_flow/snapshot.html  | 276 ++++++++++++++
 docs/_modules/mgrid/power_flow/type.html      |   3 +-
 docs/_modules/mgrid/transformation.html       |  68 ++--
 docs/_sources/graph.rst.txt                   |   6 +-
 docs/_sources/grid.rst.txt                    |   6 +-
 docs/_sources/index.rst.txt                   |   3 +-
 docs/_sources/snapshots.rst.txt               |  15 +
 docs/bibliography.html                        |   7 +-
 docs/genindex.html                            | 155 +++++---
 docs/graph.html                               | 150 ++++----
 docs/grid.html                                | 109 ++++--
 docs/index.html                               |  15 +-
 docs/objects.inv                              | Bin 1390 -> 1551 bytes
 docs/power_flow.html                          |  13 +-
 docs/py-modindex.html                         |  17 +-
 docs/search.html                              |   3 +-
 docs/searchindex.js                           |   2 +-
 docs/snapshots.html                           | 339 ++++++++++++++++++
 docs/transformation.html                      |  15 +-
 docs_raw/graph.rst                            |   6 +-
 docs_raw/grid.rst                             |   6 +-
 docs_raw/index.rst                            |   3 +-
 docs_raw/snapshots.rst                        |  15 +
 mgrid/__init__.py                             |   2 +-
 pyproject.toml                                |   3 +-
 setup.py                                      |   9 +
 35 files changed, 1386 insertions(+), 285 deletions(-)
 rename docs/_modules/mgrid/graph/{planar.html => geographic.html} (87%)
 rename docs/_modules/mgrid/grid/{planar.html => geographic.html} (88%)
 create mode 100644 docs/_modules/mgrid/power_flow/series.html
 create mode 100644 docs/_modules/mgrid/power_flow/snapshot.html
 create mode 100644 docs/_sources/snapshots.rst.txt
 create mode 100644 docs/snapshots.html
 create mode 100644 docs_raw/snapshots.rst
 create mode 100644 setup.py

diff --git a/docs/_modules/index.html b/docs/_modules/index.html
index 08070a3..25b6ef9 100644
--- a/docs/_modules/index.html
+++ b/docs/_modules/index.html
@@ -89,8 +89,9 @@
               <ul>
 <li class="toctree-l1"><a class="reference internal" href="../graph.html">Graph Theoretic Model</a></li>
 <li class="toctree-l1"><a class="reference internal" href="../grid.html">Power Grid</a></li>
-<li class="toctree-l1"><a class="reference internal" href="../power_flow.html">Power Flow Calculation</a></li>
 <li class="toctree-l1"><a class="reference internal" href="../transformation.html">Transformation</a></li>
+<li class="toctree-l1"><a class="reference internal" href="../power_flow.html">Power Flow Calculation</a></li>
+<li class="toctree-l1"><a class="reference internal" href="../snapshots.html">Snapshot</a></li>
 </ul>
 <ul>
 <li class="toctree-l1"><a class="reference internal" href="../bibliography.html">Bibliography</a></li>
@@ -158,13 +159,15 @@
            <div itemprop="articleBody">
 
   <h1>All modules for which code is available</h1>
-<ul><li><a href="mgrid/graph/planar.html">mgrid.graph.planar</a></li>
+<ul><li><a href="mgrid/graph/geographic.html">mgrid.graph.geographic</a></li>
 <li><a href="mgrid/graph/supra.html">mgrid.graph.supra</a></li>
-<li><a href="mgrid/grid/planar.html">mgrid.grid.planar</a></li>
+<li><a href="mgrid/grid/geographic.html">mgrid.grid.geographic</a></li>
 <li><a href="mgrid/grid/supra.html">mgrid.grid.supra</a></li>
 <li><a href="mgrid/power_flow/conversion.html">mgrid.power_flow.conversion</a></li>
 <li><a href="mgrid/power_flow/delivery.html">mgrid.power_flow.delivery</a></li>
 <li><a href="mgrid/power_flow/pandapower.html">mgrid.power_flow.pandapower</a></li>
+<li><a href="mgrid/power_flow/series.html">mgrid.power_flow.series</a></li>
+<li><a href="mgrid/power_flow/snapshot.html">mgrid.power_flow.snapshot</a></li>
 <li><a href="mgrid/power_flow/type.html">mgrid.power_flow.type</a></li>
 <li><a href="mgrid/transformation.html">mgrid.transformation</a></li>
 </ul>
diff --git a/docs/_modules/mgrid/graph/planar.html b/docs/_modules/mgrid/graph/geographic.html
similarity index 87%
rename from docs/_modules/mgrid/graph/planar.html
rename to docs/_modules/mgrid/graph/geographic.html
index 142b3fa..84f07c0 100644
--- a/docs/_modules/mgrid/graph/planar.html
+++ b/docs/_modules/mgrid/graph/geographic.html
@@ -7,7 +7,7 @@
 
   <meta name="viewport" content="width=device-width, initial-scale=1.0" />
 
-  <title>mgrid.graph.planar &mdash; mgrid v0.2.5 documentation</title>
+  <title>mgrid.graph.geographic &mdash; mgrid v0.2.5 documentation</title>
 
 
 
@@ -89,8 +89,9 @@
               <ul>
 <li class="toctree-l1"><a class="reference internal" href="../../../graph.html">Graph Theoretic Model</a></li>
 <li class="toctree-l1"><a class="reference internal" href="../../../grid.html">Power Grid</a></li>
-<li class="toctree-l1"><a class="reference internal" href="../../../power_flow.html">Power Flow Calculation</a></li>
 <li class="toctree-l1"><a class="reference internal" href="../../../transformation.html">Transformation</a></li>
+<li class="toctree-l1"><a class="reference internal" href="../../../power_flow.html">Power Flow Calculation</a></li>
+<li class="toctree-l1"><a class="reference internal" href="../../../snapshots.html">Snapshot</a></li>
 </ul>
 <ul>
 <li class="toctree-l1"><a class="reference internal" href="../../../bibliography.html">Bibliography</a></li>
@@ -144,7 +145,7 @@
 
           <li><a href="../../index.html">Module code</a> &raquo;</li>
 
-      <li>mgrid.graph.planar</li>
+      <li>mgrid.graph.geographic</li>
 
 
       <li class="wy-breadcrumbs-aside">
@@ -159,11 +160,15 @@
           <div role="main" class="document" itemscope="itemscope" itemtype="http://schema.org/Article">
            <div itemprop="articleBody">
 
-  <h1>Source code for mgrid.graph.planar</h1><div class="highlight"><pre>
-<span></span><span class="sd">&quot;&quot;&quot;A class for planar graph corresponding to a multilayer network.</span>
+  <h1>Source code for mgrid.graph.geographic</h1><div class="highlight"><pre>
+<span></span><span class="sd">&quot;&quot;&quot;A class for geographic graph corresponding to a multilayer network.</span>
 
-<span class="sd">All the nodes and edges in a planar graph can have geographical</span>
-<span class="sd">attributes.</span>
+<span class="sd">Geographic graph is a unique concept in this project. Due to the fact</span>
+<span class="sd">that there is no duplicated intra-nodes in different layers, all the</span>
+<span class="sd">intra-edges can be included in one simple graph (without parallel edge).</span>
+<span class="sd">Furthermore, inter-nodes represent transformers in power systems, so</span>
+<span class="sd">they are geographical points. That is, all the nodes and edges in a</span>
+<span class="sd">planar graph have geographical attributes.</span>
 <span class="sd">&quot;&quot;&quot;</span>
 <span class="kn">from</span> <span class="nn">itertools</span> <span class="kn">import</span> <span class="n">chain</span>
 <span class="kn">from</span> <span class="nn">typing</span> <span class="kn">import</span> <span class="n">Optional</span><span class="p">,</span> <span class="n">Set</span><span class="p">,</span> <span class="n">Tuple</span>
@@ -178,14 +183,13 @@ <h1>Source code for mgrid.graph.planar</h1><div class="highlight"><pre>
 <span class="n">COLUMNS_DI</span> <span class="o">=</span> <span class="p">[</span><span class="s2">&quot;source&quot;</span><span class="p">,</span> <span class="s2">&quot;target&quot;</span><span class="p">]</span>
 
 
-<div class="viewcode-block" id="PlanarGraph"><a class="viewcode-back" href="../../../graph.html#mgrid.graph.planar.PlanarGraph">[docs]</a><span class="k">class</span> <span class="nc">PlanarGraph</span><span class="p">(</span><span class="n">nx</span><span class="o">.</span><span class="n">DiGraph</span><span class="p">):</span>
-    <span class="sd">&quot;&quot;&quot;Multilayer network in form of planar graph.</span>
+<div class="viewcode-block" id="GeoGraph"><a class="viewcode-back" href="../../../graph.html#mgrid.graph.geographic.GeoGraph">[docs]</a><span class="k">class</span> <span class="nc">GeoGraph</span><span class="p">(</span><span class="n">nx</span><span class="o">.</span><span class="n">DiGraph</span><span class="p">):</span>
+    <span class="sd">&quot;&quot;&quot;Multilayer network as a planar graph.</span>
 
 <span class="sd">    Note:</span>
-<span class="sd">        There are two kinds of nodes, inter-nodes and planar nodes. If</span>
-<span class="sd">        an inter-node is isolated in some layer, it cannot be recognised</span>
-<span class="sd">        directly. Use method ``add_inter_node`` to specify those</span>
-<span class="sd">        inter-nodes.</span>
+<span class="sd">        ``DiGraph`` from ``networkx`` is inherited, in order to modify</span>
+<span class="sd">        terminals of edges directly. The order of edge terminals</span>
+<span class="sd">        returned by ``Graph`` class is not consistent.</span>
 
 <span class="sd">    Attributes:</span>
 <span class="sd">        inter_nodes (DataFrame): information on inter-nodes.</span>
@@ -207,7 +211,7 @@ <h1>Source code for mgrid.graph.planar</h1><div class="highlight"><pre>
 <span class="sd">                name, object, layer names</span>
 <span class="sd">    &quot;&quot;&quot;</span>
 
-<div class="viewcode-block" id="PlanarGraph.__init__"><a class="viewcode-back" href="../../../graph.html#mgrid.graph.planar.PlanarGraph.__init__">[docs]</a>    <span class="k">def</span> <span class="fm">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">dg</span><span class="p">:</span> <span class="n">Optional</span><span class="p">[</span><span class="n">nx</span><span class="o">.</span><span class="n">DiGraph</span><span class="p">]</span> <span class="o">=</span> <span class="kc">None</span><span class="p">):</span>
+<div class="viewcode-block" id="GeoGraph.__init__"><a class="viewcode-back" href="../../../graph.html#mgrid.graph.geographic.GeoGraph.__init__">[docs]</a>    <span class="k">def</span> <span class="fm">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">dg</span><span class="p">:</span> <span class="n">Optional</span><span class="p">[</span><span class="n">nx</span><span class="o">.</span><span class="n">DiGraph</span><span class="p">]</span> <span class="o">=</span> <span class="kc">None</span><span class="p">):</span>
         <span class="sd">&quot;&quot;&quot;Init an empty directed graph or from existing directed graph.</span>
 
 <span class="sd">        Args:</span>
@@ -237,7 +241,7 @@ <h1>Source code for mgrid.graph.planar</h1><div class="highlight"><pre>
         <span class="k">else</span><span class="p">:</span>
             <span class="bp">self</span><span class="o">.</span><span class="n">layers</span> <span class="o">=</span> <span class="nb">set</span><span class="p">()</span></div>
 
-<div class="viewcode-block" id="PlanarGraph.from_edgelist"><a class="viewcode-back" href="../../../graph.html#mgrid.graph.planar.PlanarGraph.from_edgelist">[docs]</a>    <span class="nd">@classmethod</span>
+<div class="viewcode-block" id="GeoGraph.from_edgelist"><a class="viewcode-back" href="../../../graph.html#mgrid.graph.geographic.GeoGraph.from_edgelist">[docs]</a>    <span class="nd">@classmethod</span>
     <span class="k">def</span> <span class="nf">from_edgelist</span><span class="p">(</span>
         <span class="bp">cls</span><span class="p">,</span>
         <span class="n">df</span><span class="p">:</span> <span class="n">DataFrame</span><span class="p">,</span>
@@ -297,7 +301,6 @@ <h1>Source code for mgrid.graph.planar</h1><div class="highlight"><pre>
 <span class="sd">                name (index), name of the node</span>
 <span class="sd">                upper, int64, upper layer of the inter-edge</span>
 <span class="sd">                lower, int64, lower layer of the inter-edge</span>
-
 <span class="sd">        &quot;&quot;&quot;</span>
         <span class="n">res_dict</span> <span class="o">=</span> <span class="p">{}</span>
         <span class="k">for</span> <span class="n">node</span> <span class="ow">in</span> <span class="bp">self</span><span class="o">.</span><span class="n">nodes</span><span class="p">:</span>
@@ -323,14 +326,13 @@ <h1>Source code for mgrid.graph.planar</h1><div class="highlight"><pre>
         <span class="sd">&quot;&quot;&quot;Gather all the intra-nodes in a dataframe.</span>
 
 <span class="sd">        Returns:</span>
-<span class="sd">            A dataframe for intra-nodes.</span>
+<span class="sd">            Information on intra-nodes.</span>
 
 <span class="sd">            .. csv-table::</span>
 <span class="sd">                :header: name, dtype, definition</span>
 
 <span class="sd">                name (index), object, node name</span>
 <span class="sd">                layer, int64, to which layer the node belongs</span>
-
 <span class="sd">        &quot;&quot;&quot;</span>
         <span class="n">inter_nodes</span> <span class="o">=</span> <span class="nb">set</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">inter_nodes</span><span class="o">.</span><span class="n">index</span><span class="p">)</span>
         <span class="n">intra_nodes</span> <span class="o">=</span> <span class="p">[</span><span class="n">node</span> <span class="k">for</span> <span class="n">node</span> <span class="ow">in</span> <span class="bp">self</span><span class="o">.</span><span class="n">nodes</span> <span class="k">if</span> <span class="n">node</span> <span class="ow">not</span> <span class="ow">in</span> <span class="n">inter_nodes</span><span class="p">]</span>
@@ -342,7 +344,7 @@ <h1>Source code for mgrid.graph.planar</h1><div class="highlight"><pre>
         <span class="n">res</span><span class="o">.</span><span class="n">index</span><span class="o">.</span><span class="n">name</span> <span class="o">=</span> <span class="s2">&quot;name&quot;</span>
         <span class="k">return</span> <span class="n">res</span>
 
-<div class="viewcode-block" id="PlanarGraph.layer_edges"><a class="viewcode-back" href="../../../graph.html#mgrid.graph.planar.PlanarGraph.layer_edges">[docs]</a>    <span class="k">def</span> <span class="nf">layer_edges</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">layer</span><span class="p">:</span> <span class="nb">int</span><span class="p">)</span> <span class="o">-&gt;</span> <span class="n">Set</span><span class="p">[</span><span class="nb">tuple</span><span class="p">]:</span>
+<div class="viewcode-block" id="GeoGraph.layer_edges"><a class="viewcode-back" href="../../../graph.html#mgrid.graph.geographic.GeoGraph.layer_edges">[docs]</a>    <span class="k">def</span> <span class="nf">layer_edges</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">layer</span><span class="p">:</span> <span class="nb">int</span><span class="p">)</span> <span class="o">-&gt;</span> <span class="n">Set</span><span class="p">[</span><span class="nb">tuple</span><span class="p">]:</span>
         <span class="sd">&quot;&quot;&quot;Gather all the edges and edge attributes in one layer.</span>
 
 <span class="sd">        Args:</span>
@@ -358,7 +360,7 @@ <h1>Source code for mgrid.graph.planar</h1><div class="highlight"><pre>
             <span class="n">res</span> <span class="o">=</span> <span class="kc">None</span>
         <span class="k">return</span> <span class="n">res</span></div>
 
-<div class="viewcode-block" id="PlanarGraph.layer_graph"><a class="viewcode-back" href="../../../graph.html#mgrid.graph.planar.PlanarGraph.layer_graph">[docs]</a>    <span class="k">def</span> <span class="nf">layer_graph</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">layer</span><span class="p">:</span> <span class="nb">int</span><span class="p">)</span> <span class="o">-&gt;</span> <span class="n">nx</span><span class="o">.</span><span class="n">DiGraph</span><span class="p">:</span>
+<div class="viewcode-block" id="GeoGraph.layer_graph"><a class="viewcode-back" href="../../../graph.html#mgrid.graph.geographic.GeoGraph.layer_graph">[docs]</a>    <span class="k">def</span> <span class="nf">layer_graph</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">layer</span><span class="p">:</span> <span class="nb">int</span><span class="p">)</span> <span class="o">-&gt;</span> <span class="n">nx</span><span class="o">.</span><span class="n">DiGraph</span><span class="p">:</span>
         <span class="sd">&quot;&quot;&quot;Build a directed graph for one layer.</span>
 
 <span class="sd">        Note:</span>
@@ -378,7 +380,7 @@ <h1>Source code for mgrid.graph.planar</h1><div class="highlight"><pre>
             <span class="n">res</span> <span class="o">=</span> <span class="kc">None</span>
         <span class="k">return</span> <span class="n">res</span></div>
 
-<div class="viewcode-block" id="PlanarGraph.find_layer"><a class="viewcode-back" href="../../../graph.html#mgrid.graph.planar.PlanarGraph.find_layer">[docs]</a>    <span class="k">def</span> <span class="nf">find_layer</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">node</span><span class="p">:</span> <span class="nb">str</span><span class="p">)</span> <span class="o">-&gt;</span> <span class="n">Tuple</span><span class="p">[</span><span class="nb">int</span><span class="p">,</span> <span class="nb">int</span><span class="p">]:</span>
+<div class="viewcode-block" id="GeoGraph.find_layer"><a class="viewcode-back" href="../../../graph.html#mgrid.graph.geographic.GeoGraph.find_layer">[docs]</a>    <span class="k">def</span> <span class="nf">find_layer</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">node</span><span class="p">:</span> <span class="nb">str</span><span class="p">)</span> <span class="o">-&gt;</span> <span class="n">Tuple</span><span class="p">[</span><span class="nb">int</span><span class="p">,</span> <span class="nb">int</span><span class="p">]:</span>
         <span class="sd">&quot;&quot;&quot;Find layer(s) of a given node.</span>
 
 <span class="sd">        Note:</span>
@@ -410,12 +412,12 @@ <h1>Source code for mgrid.graph.planar</h1><div class="highlight"><pre>
 
         <span class="k">return</span> <span class="p">(</span><span class="n">upper</span><span class="p">,</span> <span class="n">lower</span><span class="p">)</span></div>
 
-<div class="viewcode-block" id="PlanarGraph.add_inter_node"><a class="viewcode-back" href="../../../graph.html#mgrid.graph.planar.PlanarGraph.add_inter_node">[docs]</a>    <span class="k">def</span> <span class="nf">add_inter_node</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">name</span><span class="p">:</span> <span class="nb">str</span><span class="p">,</span> <span class="n">upper</span><span class="p">:</span> <span class="n">Optional</span><span class="p">[</span><span class="nb">bool</span><span class="p">]</span> <span class="o">=</span> <span class="kc">True</span><span class="p">):</span>
-        <span class="sd">&quot;&quot;&quot;Specify a planar node as an inter-node with an adjacent layer.</span>
+<div class="viewcode-block" id="GeoGraph.add_inter_node"><a class="viewcode-back" href="../../../graph.html#mgrid.graph.geographic.GeoGraph.add_inter_node">[docs]</a>    <span class="k">def</span> <span class="nf">add_inter_node</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">name</span><span class="p">:</span> <span class="nb">str</span><span class="p">,</span> <span class="n">upper</span><span class="p">:</span> <span class="n">Optional</span><span class="p">[</span><span class="nb">bool</span><span class="p">]</span> <span class="o">=</span> <span class="kc">True</span><span class="p">):</span>
+        <span class="sd">&quot;&quot;&quot;Specify a planar node as inter-node with an adjacent layer.</span>
 
-<span class="sd">        Sometimes, one terminal of an inter-edge is an isolated node in some</span>
-<span class="sd">        layer, then it will not be recognised as an inter-node. It must be</span>
-<span class="sd">        specified manually.</span>
+<span class="sd">        Sometimes, one terminal of an inter-edge is an isolated node in</span>
+<span class="sd">        some layer, then it will not be recognised as an inter-node. It</span>
+<span class="sd">        must be specified manually.</span>
 
 <span class="sd">        Warning:</span>
 <span class="sd">            Upper layer has a smaller integer index.</span>
diff --git a/docs/_modules/mgrid/graph/supra.html b/docs/_modules/mgrid/graph/supra.html
index 66a0939..3081ab1 100644
--- a/docs/_modules/mgrid/graph/supra.html
+++ b/docs/_modules/mgrid/graph/supra.html
@@ -89,8 +89,9 @@
               <ul>
 <li class="toctree-l1"><a class="reference internal" href="../../../graph.html">Graph Theoretic Model</a></li>
 <li class="toctree-l1"><a class="reference internal" href="../../../grid.html">Power Grid</a></li>
-<li class="toctree-l1"><a class="reference internal" href="../../../power_flow.html">Power Flow Calculation</a></li>
 <li class="toctree-l1"><a class="reference internal" href="../../../transformation.html">Transformation</a></li>
+<li class="toctree-l1"><a class="reference internal" href="../../../power_flow.html">Power Flow Calculation</a></li>
+<li class="toctree-l1"><a class="reference internal" href="../../../snapshots.html">Snapshot</a></li>
 </ul>
 <ul>
 <li class="toctree-l1"><a class="reference internal" href="../../../bibliography.html">Bibliography</a></li>
@@ -160,10 +161,12 @@
            <div itemprop="articleBody">
 
   <h1>Source code for mgrid.graph.supra</h1><div class="highlight"><pre>
-<span></span><span class="sd">&quot;&quot;&quot;Class for multilayer network in supra graph format.&quot;&quot;&quot;</span>
+<span></span><span class="sd">&quot;&quot;&quot;Class for multilayer network in supra-graph format.&quot;&quot;&quot;</span>
 <span class="kn">from</span> <span class="nn">typing</span> <span class="kn">import</span> <span class="n">Optional</span>
 
 <span class="kn">import</span> <span class="nn">networkx</span> <span class="k">as</span> <span class="nn">nx</span>
+<span class="kn">import</span> <span class="nn">pandas</span> <span class="k">as</span> <span class="nn">pd</span>
+<span class="kn">from</span> <span class="nn">pandas.core.frame</span> <span class="kn">import</span> <span class="n">DataFrame</span>
 
 
 <div class="viewcode-block" id="SupraGraph"><a class="viewcode-back" href="../../../graph.html#mgrid.graph.supra.SupraGraph">[docs]</a><span class="k">class</span> <span class="nc">SupraGraph</span><span class="p">(</span><span class="n">nx</span><span class="o">.</span><span class="n">DiGraph</span><span class="p">):</span>
@@ -207,16 +210,6 @@ <h1>Source code for mgrid.graph.supra</h1><div class="highlight"><pre>
 <span class="sd">                lower, int64, integer index of lower layer</span>
 <span class="sd">                source, object, source node in supra graph</span>
 <span class="sd">                target, object, target node in supra graph</span>
-
-<span class="sd">        nodelist (DataFrame): sorted nodelist containing layer</span>
-<span class="sd">            information.</span>
-
-<span class="sd">            .. csv-table::</span>
-<span class="sd">                :header: name, dtype, definition</span>
-
-<span class="sd">                node (index), object, node name</span>
-<span class="sd">                idx, int64, layer to which node belongs</span>
-<span class="sd">                name, object, layer name</span>
 <span class="sd">    &quot;&quot;&quot;</span>
 
 <div class="viewcode-block" id="SupraGraph.__init__"><a class="viewcode-back" href="../../../graph.html#mgrid.graph.supra.SupraGraph.__init__">[docs]</a>    <span class="k">def</span> <span class="fm">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">dg</span><span class="p">:</span> <span class="n">Optional</span><span class="p">[</span><span class="n">nx</span><span class="o">.</span><span class="n">DiGraph</span><span class="p">]</span> <span class="o">=</span> <span class="kc">None</span><span class="p">):</span>
@@ -238,8 +231,32 @@ <h1>Source code for mgrid.graph.supra</h1><div class="highlight"><pre>
         <span class="c1"># nx.freeze(self)</span>
 
         <span class="bp">self</span><span class="o">.</span><span class="n">intra_edges</span> <span class="o">=</span> <span class="kc">None</span>
-        <span class="bp">self</span><span class="o">.</span><span class="n">inter_edges</span> <span class="o">=</span> <span class="kc">None</span>
-        <span class="bp">self</span><span class="o">.</span><span class="n">nodelist</span> <span class="o">=</span> <span class="kc">None</span></div></div>
+        <span class="bp">self</span><span class="o">.</span><span class="n">inter_edges</span> <span class="o">=</span> <span class="kc">None</span></div>
+
+    <span class="nd">@property</span>
+    <span class="k">def</span> <span class="nf">nodes_new</span><span class="p">(</span><span class="bp">self</span><span class="p">)</span> <span class="o">-&gt;</span> <span class="n">DataFrame</span><span class="p">:</span>
+        <span class="sd">&quot;&quot;&quot;Gather information on terminals of inter-edges.</span>
+
+<span class="sd">        Returns:</span>
+<span class="sd">            Correspondance between original nodes, layers and buses for</span>
+<span class="sd">            terminals of inter-edges.</span>
+
+<span class="sd">            .. csv-table::</span>
+<span class="sd">                :header: name, dtype, definition</span>
+
+<span class="sd">                origin (index), object, node in geographic graph</span>
+<span class="sd">                layer (index), int64, to which layer the node belongs</span>
+<span class="sd">                bus, object, node name in supra graph</span>
+<span class="sd">        &quot;&quot;&quot;</span>
+        <span class="n">data</span> <span class="o">=</span> <span class="p">{}</span>
+        <span class="k">for</span> <span class="n">node</span> <span class="ow">in</span> <span class="bp">self</span><span class="o">.</span><span class="n">nodes</span><span class="o">.</span><span class="n">data</span><span class="p">():</span>
+            <span class="k">if</span> <span class="s2">&quot;origin&quot;</span> <span class="ow">in</span> <span class="n">node</span><span class="p">[</span><span class="mi">1</span><span class="p">]:</span>
+                <span class="n">data</span><span class="p">[(</span><span class="n">node</span><span class="p">[</span><span class="mi">1</span><span class="p">][</span><span class="s2">&quot;origin&quot;</span><span class="p">],</span> <span class="n">node</span><span class="p">[</span><span class="mi">1</span><span class="p">][</span><span class="s2">&quot;layer&quot;</span><span class="p">])]</span> <span class="o">=</span> <span class="n">node</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span>
+        <span class="n">res</span> <span class="o">=</span> <span class="n">pd</span><span class="o">.</span><span class="n">DataFrame</span><span class="o">.</span><span class="n">from_dict</span><span class="p">(</span><span class="n">data</span><span class="p">,</span> <span class="n">orient</span><span class="o">=</span><span class="s2">&quot;index&quot;</span><span class="p">,</span> <span class="n">columns</span><span class="o">=</span><span class="p">[</span><span class="s2">&quot;bus&quot;</span><span class="p">])</span>
+        <span class="n">res</span><span class="o">.</span><span class="n">index</span> <span class="o">=</span> <span class="n">pd</span><span class="o">.</span><span class="n">MultiIndex</span><span class="o">.</span><span class="n">from_tuples</span><span class="p">(</span>
+            <span class="n">res</span><span class="o">.</span><span class="n">index</span><span class="p">,</span> <span class="n">names</span><span class="o">=</span><span class="p">[</span><span class="s2">&quot;origin&quot;</span><span class="p">,</span> <span class="s2">&quot;layer&quot;</span><span class="p">]</span>
+        <span class="p">)</span>
+        <span class="k">return</span> <span class="n">res</span></div>
 </pre></div>
 
            </div>
diff --git a/docs/_modules/mgrid/grid/planar.html b/docs/_modules/mgrid/grid/geographic.html
similarity index 88%
rename from docs/_modules/mgrid/grid/planar.html
rename to docs/_modules/mgrid/grid/geographic.html
index fe92abd..381d432 100644
--- a/docs/_modules/mgrid/grid/planar.html
+++ b/docs/_modules/mgrid/grid/geographic.html
@@ -7,7 +7,7 @@
 
   <meta name="viewport" content="width=device-width, initial-scale=1.0" />
 
-  <title>mgrid.grid.planar &mdash; mgrid v0.2.5 documentation</title>
+  <title>mgrid.grid.geographic &mdash; mgrid v0.2.5 documentation</title>
 
 
 
@@ -89,8 +89,9 @@
               <ul>
 <li class="toctree-l1"><a class="reference internal" href="../../../graph.html">Graph Theoretic Model</a></li>
 <li class="toctree-l1"><a class="reference internal" href="../../../grid.html">Power Grid</a></li>
-<li class="toctree-l1"><a class="reference internal" href="../../../power_flow.html">Power Flow Calculation</a></li>
 <li class="toctree-l1"><a class="reference internal" href="../../../transformation.html">Transformation</a></li>
+<li class="toctree-l1"><a class="reference internal" href="../../../power_flow.html">Power Flow Calculation</a></li>
+<li class="toctree-l1"><a class="reference internal" href="../../../snapshots.html">Snapshot</a></li>
 </ul>
 <ul>
 <li class="toctree-l1"><a class="reference internal" href="../../../bibliography.html">Bibliography</a></li>
@@ -144,7 +145,7 @@
 
           <li><a href="../../index.html">Module code</a> &raquo;</li>
 
-      <li>mgrid.grid.planar</li>
+      <li>mgrid.grid.geographic</li>
 
 
       <li class="wy-breadcrumbs-aside">
@@ -159,7 +160,7 @@
           <div role="main" class="document" itemscope="itemscope" itemtype="http://schema.org/Article">
            <div itemprop="articleBody">
 
-  <h1>Source code for mgrid.grid.planar</h1><div class="highlight"><pre>
+  <h1>Source code for mgrid.grid.geographic</h1><div class="highlight"><pre>
 <span></span><span class="sd">&quot;&quot;&quot;Class for grid in planar graph format.&quot;&quot;&quot;</span>
 <span class="kn">from</span> <span class="nn">typing</span> <span class="kn">import</span> <span class="n">Optional</span><span class="p">,</span> <span class="n">Union</span>
 
@@ -167,18 +168,20 @@ <h1>Source code for mgrid.grid.planar</h1><div class="highlight"><pre>
 <span class="kn">import</span> <span class="nn">numpy</span> <span class="k">as</span> <span class="nn">np</span>
 <span class="kn">import</span> <span class="nn">pandas</span> <span class="k">as</span> <span class="nn">pd</span>
 
-<span class="kn">from</span> <span class="nn">mgrid.graph.planar</span> <span class="kn">import</span> <span class="n">PlanarGraph</span>
+<span class="kn">from</span> <span class="nn">mgrid.graph.geographic</span> <span class="kn">import</span> <span class="n">GeoGraph</span>
 <span class="kn">from</span> <span class="nn">mgrid.log</span> <span class="kn">import</span> <span class="n">LOGGER</span>
-<span class="kn">from</span> <span class="nn">mgrid.power_flow.conversion</span> <span class="kn">import</span> <span class="n">Ejection</span><span class="p">,</span> <span class="n">Slack</span>
+<span class="kn">from</span> <span class="nn">mgrid.power_flow.conversion</span> <span class="kn">import</span> <span class="n">Ejection</span>
 <span class="kn">from</span> <span class="nn">mgrid.power_flow.delivery</span> <span class="kn">import</span> <span class="n">Transformer</span><span class="p">,</span> <span class="n">TransformerStd</span>
 
 
-<div class="viewcode-block" id="PlanarGrid"><a class="viewcode-back" href="../../../grid.html#mgrid.grid.planar.PlanarGrid">[docs]</a><span class="k">class</span> <span class="nc">PlanarGrid</span><span class="p">(</span><span class="n">PlanarGraph</span><span class="p">):</span>
+<div class="viewcode-block" id="GeoGrid"><a class="viewcode-back" href="../../../grid.html#mgrid.grid.geographic.GeoGrid">[docs]</a><span class="k">class</span> <span class="nc">GeoGrid</span><span class="p">(</span><span class="n">GeoGraph</span><span class="p">):</span>
     <span class="sd">&quot;&quot;&quot;Model multilayer graph in plane by contracting inter-edges.</span>
 
 <span class="sd">    Note:</span>
-<span class="sd">        Voltage levels of layers must be specified by updating</span>
-<span class="sd">        ``df_layers`` manually.</span>
+<span class="sd">        - There are two kinds of nodes, inter-nodes and planar nodes. If</span>
+<span class="sd">          an inter-node is isolated in some layer, it cannot be</span>
+<span class="sd">          recognised directly.</span>
+<span class="sd">        - It is assumed that every conversion element has a unique name.</span>
 
 <span class="sd">    Attributes:</span>
 <span class="sd">        inter_nodes (DataFrame): information on inter-nodes.</span>
@@ -192,7 +195,7 @@ <h1>Source code for mgrid.grid.planar</h1><div class="highlight"><pre>
 <span class="sd">                element, object, transformer model</span>
 
 <span class="sd">        layers (Set[int]): integer indices of all the layers.</span>
-<span class="sd">        conversion (DataFrame): information on conversion elements.</span>
+<span class="sd">        conversions (DataFrame): information on conversion elements.</span>
 
 <span class="sd">            .. csv-table::</span>
 <span class="sd">                :header: name, dtype, definition</span>
@@ -223,7 +226,7 @@ <h1>Source code for mgrid.grid.planar</h1><div class="highlight"><pre>
 <span class="sd">                voltage, float64, voltage levels</span>
 <span class="sd">    &quot;&quot;&quot;</span>
 
-<div class="viewcode-block" id="PlanarGrid.__init__"><a class="viewcode-back" href="../../../grid.html#mgrid.grid.planar.PlanarGrid.__init__">[docs]</a>    <span class="k">def</span> <span class="fm">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">dg</span><span class="p">:</span> <span class="n">Optional</span><span class="p">[</span><span class="n">nx</span><span class="o">.</span><span class="n">DiGraph</span><span class="p">]</span> <span class="o">=</span> <span class="kc">None</span><span class="p">):</span>
+<div class="viewcode-block" id="GeoGrid.__init__"><a class="viewcode-back" href="../../../grid.html#mgrid.grid.geographic.GeoGrid.__init__">[docs]</a>    <span class="k">def</span> <span class="fm">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">dg</span><span class="p">:</span> <span class="n">Optional</span><span class="p">[</span><span class="n">nx</span><span class="o">.</span><span class="n">DiGraph</span><span class="p">]</span> <span class="o">=</span> <span class="kc">None</span><span class="p">):</span>
         <span class="sd">&quot;&quot;&quot;Init an empty directed graph or from existing directed graph.</span>
 
 <span class="sd">        Note:</span>
@@ -258,7 +261,7 @@ <h1>Source code for mgrid.grid.planar</h1><div class="highlight"><pre>
         <span class="c1"># Init the dictionary for element types.</span>
         <span class="bp">self</span><span class="o">.</span><span class="n">types</span> <span class="o">=</span> <span class="p">{}</span></div>
 
-<div class="viewcode-block" id="PlanarGrid.add_inter_node"><a class="viewcode-back" href="../../../grid.html#mgrid.grid.planar.PlanarGrid.add_inter_node">[docs]</a>    <span class="k">def</span> <span class="nf">add_inter_node</span><span class="p">(</span>
+<div class="viewcode-block" id="GeoGrid.add_inter_node"><a class="viewcode-back" href="../../../grid.html#mgrid.grid.geographic.GeoGrid.add_inter_node">[docs]</a>    <span class="k">def</span> <span class="nf">add_inter_node</span><span class="p">(</span>
         <span class="bp">self</span><span class="p">,</span>
         <span class="n">name</span><span class="p">:</span> <span class="nb">str</span><span class="p">,</span>
         <span class="n">element</span><span class="p">:</span> <span class="n">Union</span><span class="p">[</span><span class="n">Transformer</span><span class="p">,</span> <span class="n">TransformerStd</span><span class="p">],</span>
@@ -284,11 +287,11 @@ <h1>Source code for mgrid.grid.planar</h1><div class="highlight"><pre>
 
         <span class="bp">self</span><span class="o">.</span><span class="n">inter_nodes</span><span class="o">.</span><span class="n">loc</span><span class="p">[</span><span class="n">name</span><span class="p">,</span> <span class="s2">&quot;element&quot;</span><span class="p">]</span> <span class="o">=</span> <span class="n">element</span></div>
 
-<div class="viewcode-block" id="PlanarGrid.add_conversion"><a class="viewcode-back" href="../../../grid.html#mgrid.grid.planar.PlanarGrid.add_conversion">[docs]</a>    <span class="k">def</span> <span class="nf">add_conversion</span><span class="p">(</span>
+<div class="viewcode-block" id="GeoGrid.add_conversion"><a class="viewcode-back" href="../../../grid.html#mgrid.grid.geographic.GeoGrid.add_conversion">[docs]</a>    <span class="k">def</span> <span class="nf">add_conversion</span><span class="p">(</span>
         <span class="bp">self</span><span class="p">,</span>
         <span class="n">name</span><span class="p">:</span> <span class="nb">str</span><span class="p">,</span>
         <span class="n">node</span><span class="p">:</span> <span class="nb">str</span><span class="p">,</span>
-        <span class="n">element</span><span class="p">:</span> <span class="n">Union</span><span class="p">[</span><span class="n">Ejection</span><span class="p">,</span> <span class="n">Slack</span><span class="p">],</span>
+        <span class="n">element</span><span class="p">:</span> <span class="n">Ejection</span><span class="p">,</span>
         <span class="n">layer</span><span class="p">:</span> <span class="n">Optional</span><span class="p">[</span><span class="nb">str</span><span class="p">]</span> <span class="o">=</span> <span class="kc">None</span><span class="p">,</span>
     <span class="p">):</span>
         <span class="sd">&quot;&quot;&quot;Add a conversion element to the grid.</span>
@@ -321,6 +324,7 @@ <h1>Source code for mgrid.grid.planar</h1><div class="highlight"><pre>
                 <span class="p">{</span><span class="s2">&quot;node&quot;</span><span class="p">:</span> <span class="n">node</span><span class="p">,</span> <span class="s2">&quot;element&quot;</span><span class="p">:</span> <span class="n">element</span><span class="p">,</span> <span class="s2">&quot;layer&quot;</span><span class="p">:</span> <span class="n">layer</span><span class="p">},</span>
                 <span class="n">index</span><span class="o">=</span><span class="p">[</span><span class="n">name</span><span class="p">],</span>
             <span class="p">)</span>
+            <span class="n">_new</span><span class="o">.</span><span class="n">index</span><span class="o">.</span><span class="n">name</span> <span class="o">=</span> <span class="s2">&quot;name&quot;</span>
             <span class="bp">self</span><span class="o">.</span><span class="n">conversions</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">conversions</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="n">_new</span><span class="p">)</span>
             <span class="n">LOGGER</span><span class="o">.</span><span class="n">debug</span><span class="p">(</span>
                 <span class="sa">f</span><span class="s1">&#39;New conversion element &quot;</span><span class="si">{</span><span class="n">element</span><span class="si">}</span><span class="s1">&quot; called &quot;</span><span class="si">{</span><span class="n">name</span><span class="si">}</span><span class="s1">&quot; is &#39;</span>
diff --git a/docs/_modules/mgrid/grid/supra.html b/docs/_modules/mgrid/grid/supra.html
index 08600fd..8ebef92 100644
--- a/docs/_modules/mgrid/grid/supra.html
+++ b/docs/_modules/mgrid/grid/supra.html
@@ -89,8 +89,9 @@
               <ul>
 <li class="toctree-l1"><a class="reference internal" href="../../../graph.html">Graph Theoretic Model</a></li>
 <li class="toctree-l1"><a class="reference internal" href="../../../grid.html">Power Grid</a></li>
-<li class="toctree-l1"><a class="reference internal" href="../../../power_flow.html">Power Flow Calculation</a></li>
 <li class="toctree-l1"><a class="reference internal" href="../../../transformation.html">Transformation</a></li>
+<li class="toctree-l1"><a class="reference internal" href="../../../power_flow.html">Power Flow Calculation</a></li>
+<li class="toctree-l1"><a class="reference internal" href="../../../snapshots.html">Snapshot</a></li>
 </ul>
 <ul>
 <li class="toctree-l1"><a class="reference internal" href="../../../bibliography.html">Bibliography</a></li>
@@ -192,12 +193,20 @@ <h1>Source code for mgrid.grid.supra</h1><div class="highlight"><pre>
 <span class="sd">            .. csv-table::</span>
 <span class="sd">                :header: name, dtype, definition</span>
 
-<span class="sd">                name (index), object, name of conversion elements.</span>
-<span class="sd">                bus, object, buses to which elements are attached.</span>
-<span class="sd">                element, object, element models.</span>
+<span class="sd">                name (index), object, name of the element.</span>
+<span class="sd">                bus, object, buses to which the element is attached</span>
+<span class="sd">                element, object, model</span>
 
 <span class="sd">        types (dict): standard element types, keyed by type names.</span>
+<span class="sd">        buses (DataFrame): sorted list of buses.</span>
+
+<span class="sd">            .. csv-table::</span>
+<span class="sd">                :header: name, dtype, definition</span>
 
+<span class="sd">                node (index), object, node name</span>
+<span class="sd">                idx, int64, layer to which node belongs</span>
+<span class="sd">                layer_name, object, name of the layer</span>
+<span class="sd">                original, object, original node name</span>
 <span class="sd">    &quot;&quot;&quot;</span>
 
 <div class="viewcode-block" id="SupraGrid.__init__"><a class="viewcode-back" href="../../../grid.html#mgrid.grid.supra.SupraGrid.__init__">[docs]</a>    <span class="k">def</span> <span class="fm">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">dg</span><span class="p">:</span> <span class="n">Optional</span><span class="p">[</span><span class="n">nx</span><span class="o">.</span><span class="n">DiGraph</span><span class="p">]</span> <span class="o">=</span> <span class="kc">None</span><span class="p">):</span>
@@ -217,7 +226,8 @@ <h1>Source code for mgrid.grid.supra</h1><div class="highlight"><pre>
             <span class="nb">super</span><span class="p">()</span><span class="o">.</span><span class="fm">__init__</span><span class="p">(</span><span class="n">dg</span><span class="p">)</span>
 
         <span class="bp">self</span><span class="o">.</span><span class="n">conversions</span> <span class="o">=</span> <span class="kc">None</span>
-        <span class="bp">self</span><span class="o">.</span><span class="n">types</span> <span class="o">=</span> <span class="kc">None</span></div></div>
+        <span class="bp">self</span><span class="o">.</span><span class="n">types</span> <span class="o">=</span> <span class="kc">None</span>
+        <span class="bp">self</span><span class="o">.</span><span class="n">buses</span> <span class="o">=</span> <span class="kc">None</span></div></div>
 </pre></div>
 
            </div>
diff --git a/docs/_modules/mgrid/power_flow/conversion.html b/docs/_modules/mgrid/power_flow/conversion.html
index 7a18643..3f7eaee 100644
--- a/docs/_modules/mgrid/power_flow/conversion.html
+++ b/docs/_modules/mgrid/power_flow/conversion.html
@@ -89,8 +89,9 @@
               <ul>
 <li class="toctree-l1"><a class="reference internal" href="../../../graph.html">Graph Theoretic Model</a></li>
 <li class="toctree-l1"><a class="reference internal" href="../../../grid.html">Power Grid</a></li>
-<li class="toctree-l1"><a class="reference internal" href="../../../power_flow.html">Power Flow Calculation</a></li>
 <li class="toctree-l1"><a class="reference internal" href="../../../transformation.html">Transformation</a></li>
+<li class="toctree-l1"><a class="reference internal" href="../../../power_flow.html">Power Flow Calculation</a></li>
+<li class="toctree-l1"><a class="reference internal" href="../../../snapshots.html">Snapshot</a></li>
 </ul>
 <ul>
 <li class="toctree-l1"><a class="reference internal" href="../../../bibliography.html">Bibliography</a></li>
@@ -204,7 +205,10 @@ <h1>Source code for mgrid.power_flow.conversion</h1><div class="highlight"><pre>
         <span class="k">return</span> <span class="p">((</span><span class="bp">self</span><span class="o">.</span><span class="n">p_mw</span> <span class="o">/</span> <span class="bp">self</span><span class="o">.</span><span class="n">power_factor</span><span class="p">)</span> <span class="o">**</span> <span class="mi">2</span> <span class="o">-</span> <span class="bp">self</span><span class="o">.</span><span class="n">p_mw</span> <span class="o">**</span> <span class="mi">2</span><span class="p">)</span> <span class="o">**</span> <span class="mf">0.5</span>
 
 <div class="viewcode-block" id="Ejection.update_pandapower"><a class="viewcode-back" href="../../../power_flow.html#mgrid.power_flow.conversion.Ejection.update_pandapower">[docs]</a>    <span class="k">def</span> <span class="nf">update_pandapower</span><span class="p">(</span>
-        <span class="bp">self</span><span class="p">,</span> <span class="n">net</span><span class="p">:</span> <span class="n">pandapowerNet</span><span class="p">,</span> <span class="n">name</span><span class="p">:</span> <span class="nb">str</span><span class="p">,</span> <span class="n">bus</span><span class="p">:</span> <span class="nb">str</span><span class="p">,</span>
+        <span class="bp">self</span><span class="p">,</span>
+        <span class="n">net</span><span class="p">:</span> <span class="n">pandapowerNet</span><span class="p">,</span>
+        <span class="n">name</span><span class="p">:</span> <span class="nb">str</span><span class="p">,</span>
+        <span class="n">bus</span><span class="p">:</span> <span class="nb">str</span><span class="p">,</span>
     <span class="p">):</span>
         <span class="sd">&quot;&quot;&quot;Update a pandapower model by adding the ejection itself.</span>
 
@@ -227,7 +231,7 @@ <h1>Source code for mgrid.power_flow.conversion</h1><div class="highlight"><pre>
                 <span class="n">q_mvar</span><span class="o">=</span><span class="bp">self</span><span class="o">.</span><span class="n">q_mvar</span><span class="p">,</span>
                 <span class="n">const_i_percent</span><span class="o">=</span><span class="mi">0</span><span class="p">,</span>
                 <span class="n">const_z_percent</span><span class="o">=</span><span class="mi">0</span><span class="p">,</span>
-                <span class="n">in_service</span><span class="o">=</span><span class="kc">True</span>
+                <span class="n">in_service</span><span class="o">=</span><span class="kc">True</span><span class="p">,</span>
             <span class="p">)</span>
         <span class="k">elif</span> <span class="bp">self</span><span class="o">.</span><span class="n">p_mw</span> <span class="o">&lt;</span> <span class="mi">0</span><span class="p">:</span>
             <span class="n">pp</span><span class="o">.</span><span class="n">create_sgen</span><span class="p">(</span>
@@ -252,7 +256,10 @@ <h1>Source code for mgrid.power_flow.conversion</h1><div class="highlight"><pre>
     <span class="n">loss_factor</span><span class="p">:</span> <span class="nb">float</span>  <span class="c1">#: loss factor tan(delta) of the capacitor bank</span>
 
 <div class="viewcode-block" id="Capacitor.update_pandapower"><a class="viewcode-back" href="../../../power_flow.html#mgrid.power_flow.conversion.Capacitor.update_pandapower">[docs]</a>    <span class="k">def</span> <span class="nf">update_pandapower</span><span class="p">(</span>
-        <span class="bp">self</span><span class="p">,</span> <span class="n">net</span><span class="p">:</span> <span class="n">pandapowerNet</span><span class="p">,</span> <span class="n">name</span><span class="p">:</span> <span class="nb">str</span><span class="p">,</span> <span class="n">bus</span><span class="p">:</span> <span class="nb">str</span><span class="p">,</span>
+        <span class="bp">self</span><span class="p">,</span>
+        <span class="n">net</span><span class="p">:</span> <span class="n">pandapowerNet</span><span class="p">,</span>
+        <span class="n">name</span><span class="p">:</span> <span class="nb">str</span><span class="p">,</span>
+        <span class="n">bus</span><span class="p">:</span> <span class="nb">str</span><span class="p">,</span>
     <span class="p">):</span>
         <span class="sd">&quot;&quot;&quot;Update a pandapower model by adding the capacitor itself.</span>
 
@@ -267,7 +274,7 @@ <h1>Source code for mgrid.power_flow.conversion</h1><div class="highlight"><pre>
             <span class="n">name</span><span class="o">=</span><span class="n">name</span><span class="p">,</span>
             <span class="n">bus</span><span class="o">=</span><span class="n">bus_idx</span><span class="p">,</span>
             <span class="n">q_mvar</span><span class="o">=</span><span class="bp">self</span><span class="o">.</span><span class="n">q_mvar</span><span class="p">,</span>
-            <span class="n">loss_factor</span><span class="o">=</span><span class="bp">self</span><span class="o">.</span><span class="n">loss_factor</span>
+            <span class="n">loss_factor</span><span class="o">=</span><span class="bp">self</span><span class="o">.</span><span class="n">loss_factor</span><span class="p">,</span>
         <span class="p">)</span></div></div>
 
 
@@ -286,7 +293,10 @@ <h1>Source code for mgrid.power_flow.conversion</h1><div class="highlight"><pre>
     <span class="n">vm_pu</span><span class="p">:</span> <span class="nb">float</span> <span class="o">=</span> <span class="mf">1.0</span>  <span class="c1">#: voltage magnitude in per unit. Default to be 1.</span>
 
 <div class="viewcode-block" id="Slack.update_pandapower"><a class="viewcode-back" href="../../../power_flow.html#mgrid.power_flow.conversion.Slack.update_pandapower">[docs]</a>    <span class="k">def</span> <span class="nf">update_pandapower</span><span class="p">(</span>
-        <span class="bp">self</span><span class="p">,</span> <span class="n">net</span><span class="p">:</span> <span class="n">pandapowerNet</span><span class="p">,</span> <span class="n">name</span><span class="p">:</span> <span class="nb">str</span><span class="p">,</span> <span class="n">bus</span><span class="p">:</span> <span class="nb">str</span><span class="p">,</span>
+        <span class="bp">self</span><span class="p">,</span>
+        <span class="n">net</span><span class="p">:</span> <span class="n">pandapowerNet</span><span class="p">,</span>
+        <span class="n">name</span><span class="p">:</span> <span class="nb">str</span><span class="p">,</span>
+        <span class="n">bus</span><span class="p">:</span> <span class="nb">str</span><span class="p">,</span>
     <span class="p">):</span>
         <span class="sd">&quot;&quot;&quot;Update a pandapower model by adding the transformer itself.</span>
 
@@ -295,7 +305,8 @@ <h1>Source code for mgrid.power_flow.conversion</h1><div class="highlight"><pre>
 <span class="sd">            name: name of the external grid.</span>
 <span class="sd">            bus: the bus to which the external grid is attached.</span>
 <span class="sd">        &quot;&quot;&quot;</span>
-        <span class="n">net</span><span class="o">.</span><span class="n">add</span><span class="p">(</span><span class="s2">&quot;Generator&quot;</span><span class="p">,</span> <span class="n">name</span><span class="o">=</span><span class="n">name</span><span class="p">,</span> <span class="n">bus</span><span class="o">=</span><span class="n">bus</span><span class="p">,</span> <span class="n">control</span><span class="o">=</span><span class="s2">&quot;Slack&quot;</span><span class="p">)</span></div></div>
+        <span class="n">bus_idx</span> <span class="o">=</span> <span class="n">pp</span><span class="o">.</span><span class="n">get_element_index</span><span class="p">(</span><span class="n">net</span><span class="p">,</span> <span class="s2">&quot;bus&quot;</span><span class="p">,</span> <span class="n">bus</span><span class="p">)</span>
+        <span class="n">pp</span><span class="o">.</span><span class="n">create_ext_grid</span><span class="p">(</span><span class="n">net</span><span class="p">,</span> <span class="n">name</span><span class="o">=</span><span class="n">name</span><span class="p">,</span> <span class="n">bus</span><span class="o">=</span><span class="n">bus_idx</span><span class="p">)</span></div></div>
 
 
 <div class="viewcode-block" id="SlackMulti"><a class="viewcode-back" href="../../../power_flow.html#mgrid.power_flow.conversion.SlackMulti">[docs]</a><span class="nd">@dataclass</span>
diff --git a/docs/_modules/mgrid/power_flow/delivery.html b/docs/_modules/mgrid/power_flow/delivery.html
index bac0dbf..580ca82 100644
--- a/docs/_modules/mgrid/power_flow/delivery.html
+++ b/docs/_modules/mgrid/power_flow/delivery.html
@@ -89,8 +89,9 @@
               <ul>
 <li class="toctree-l1"><a class="reference internal" href="../../../graph.html">Graph Theoretic Model</a></li>
 <li class="toctree-l1"><a class="reference internal" href="../../../grid.html">Power Grid</a></li>
-<li class="toctree-l1"><a class="reference internal" href="../../../power_flow.html">Power Flow Calculation</a></li>
 <li class="toctree-l1"><a class="reference internal" href="../../../transformation.html">Transformation</a></li>
+<li class="toctree-l1"><a class="reference internal" href="../../../power_flow.html">Power Flow Calculation</a></li>
+<li class="toctree-l1"><a class="reference internal" href="../../../snapshots.html">Snapshot</a></li>
 </ul>
 <ul>
 <li class="toctree-l1"><a class="reference internal" href="../../../bibliography.html">Bibliography</a></li>
diff --git a/docs/_modules/mgrid/power_flow/pandapower.html b/docs/_modules/mgrid/power_flow/pandapower.html
index f8c8b89..8c9a05c 100644
--- a/docs/_modules/mgrid/power_flow/pandapower.html
+++ b/docs/_modules/mgrid/power_flow/pandapower.html
@@ -89,8 +89,9 @@
               <ul>
 <li class="toctree-l1"><a class="reference internal" href="../../../graph.html">Graph Theoretic Model</a></li>
 <li class="toctree-l1"><a class="reference internal" href="../../../grid.html">Power Grid</a></li>
-<li class="toctree-l1"><a class="reference internal" href="../../../power_flow.html">Power Flow Calculation</a></li>
 <li class="toctree-l1"><a class="reference internal" href="../../../transformation.html">Transformation</a></li>
+<li class="toctree-l1"><a class="reference internal" href="../../../power_flow.html">Power Flow Calculation</a></li>
+<li class="toctree-l1"><a class="reference internal" href="../../../snapshots.html">Snapshot</a></li>
 </ul>
 <ul>
 <li class="toctree-l1"><a class="reference internal" href="../../../bibliography.html">Bibliography</a></li>
@@ -214,7 +215,7 @@ <h1>Source code for mgrid.power_flow.pandapower</h1><div class="highlight"><pre>
         <span class="n">std_type</span><span class="o">.</span><span class="n">update_pandapower</span><span class="p">(</span><span class="n">net</span><span class="p">,</span> <span class="n">key</span><span class="p">)</span>
 
     <span class="c1"># Add all the buses.</span>
-    <span class="k">for</span> <span class="n">node</span><span class="p">,</span> <span class="n">row</span> <span class="ow">in</span> <span class="n">supra</span><span class="o">.</span><span class="n">nodelist</span><span class="o">.</span><span class="n">iterrows</span><span class="p">():</span>
+    <span class="k">for</span> <span class="n">node</span><span class="p">,</span> <span class="n">row</span> <span class="ow">in</span> <span class="n">supra</span><span class="o">.</span><span class="n">buses</span><span class="o">.</span><span class="n">iterrows</span><span class="p">():</span>
         <span class="n">pp</span><span class="o">.</span><span class="n">create_bus</span><span class="p">(</span><span class="n">net</span><span class="p">,</span> <span class="n">name</span><span class="o">=</span><span class="n">node</span><span class="p">,</span> <span class="n">vn_kv</span><span class="o">=</span><span class="n">row</span><span class="p">[</span><span class="s2">&quot;voltage&quot;</span><span class="p">])</span>
 
     <span class="c1"># Add all the delivery elements.</span>
diff --git a/docs/_modules/mgrid/power_flow/series.html b/docs/_modules/mgrid/power_flow/series.html
new file mode 100644
index 0000000..4ad9040
--- /dev/null
+++ b/docs/_modules/mgrid/power_flow/series.html
@@ -0,0 +1,232 @@
+
+
+<!DOCTYPE html>
+<html class="writer-html5" lang="en" >
+<head>
+  <meta charset="utf-8" />
+
+  <meta name="viewport" content="width=device-width, initial-scale=1.0" />
+
+  <title>mgrid.power_flow.series &mdash; mgrid v0.2.5 documentation</title>
+
+
+
+  <link rel="stylesheet" href="../../../_static/css/theme.css" type="text/css" />
+  <link rel="stylesheet" href="../../../_static/pygments.css" type="text/css" />
+
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+
+  <!--[if lt IE 9]>
+    <script src="../../../_static/js/html5shiv.min.js"></script>
+  <![endif]-->
+
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+      <script type="text/javascript" id="documentation_options" data-url_root="../../../" src="../../../_static/documentation_options.js"></script>
+        <script src="../../../_static/jquery.js"></script>
+        <script src="../../../_static/underscore.js"></script>
+        <script src="../../../_static/doctools.js"></script>
+
+    <script type="text/javascript" src="../../../_static/js/theme.js"></script>
+
+
+    <link rel="index" title="Index" href="../../../genindex.html" />
+    <link rel="search" title="Search" href="../../../search.html" />
+</head>
+
+<body class="wy-body-for-nav">
+
+
+  <div class="wy-grid-for-nav">
+
+    <nav data-toggle="wy-nav-shift" class="wy-nav-side">
+      <div class="wy-side-scroll">
+        <div class="wy-side-nav-search" >
+
+    <a href="https://github.com/edxu96/mgrid/tree/main/docs_raw">documentation source</a> |
+    <a href="https://github.com/edxu96/mgrid">repository</a>
+
+
+
+            <a href="../../../index.html" class="icon icon-home"> mgrid
+
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+          </a>
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+<div role="search">
+  <form id="rtd-search-form" class="wy-form" action="../../../search.html" method="get">
+    <input type="text" name="q" placeholder="Search docs" />
+    <input type="hidden" name="check_keywords" value="yes" />
+    <input type="hidden" name="area" value="default" />
+  </form>
+</div>
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+        </div>
+
+
+        <div class="wy-menu wy-menu-vertical" data-spy="affix" role="navigation" aria-label="main navigation">
+
+
+
+
+
+
+              <ul>
+<li class="toctree-l1"><a class="reference internal" href="../../../graph.html">Graph Theoretic Model</a></li>
+<li class="toctree-l1"><a class="reference internal" href="../../../grid.html">Power Grid</a></li>
+<li class="toctree-l1"><a class="reference internal" href="../../../transformation.html">Transformation</a></li>
+<li class="toctree-l1"><a class="reference internal" href="../../../power_flow.html">Power Flow Calculation</a></li>
+<li class="toctree-l1"><a class="reference internal" href="../../../snapshots.html">Snapshot</a></li>
+</ul>
+<ul>
+<li class="toctree-l1"><a class="reference internal" href="../../../bibliography.html">Bibliography</a></li>
+</ul>
+
+
+
+        </div>
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+      </div>
+    </nav>
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+    <section data-toggle="wy-nav-shift" class="wy-nav-content-wrap">
+
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+      <nav class="wy-nav-top" aria-label="top navigation">
+
+          <i data-toggle="wy-nav-top" class="fa fa-bars"></i>
+          <a href="../../../index.html">mgrid</a>
+
+      </nav>
+
+
+      <div class="wy-nav-content">
+
+        <div class="rst-content">
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+
+
+
+<div role="navigation" aria-label="breadcrumbs navigation">
+
+  <ul class="wy-breadcrumbs">
+
+      <li><a href="../../../index.html" class="icon icon-home"></a> &raquo;</li>
+
+          <li><a href="../../index.html">Module code</a> &raquo;</li>
+
+      <li>mgrid.power_flow.series</li>
+
+
+      <li class="wy-breadcrumbs-aside">
+
+      </li>
+
+  </ul>
+
+
+  <hr/>
+</div>
+          <div role="main" class="document" itemscope="itemscope" itemtype="http://schema.org/Article">
+           <div itemprop="articleBody">
+
+  <h1>Source code for mgrid.power_flow.series</h1><div class="highlight"><pre>
+<span></span><span class="sd">&quot;&quot;&quot;Class for building a series of snapshots.</span>
+
+<span class="sd">A ``GeoGrid`` or ``SupraGrid`` object will serve as the default snapshot.</span>
+<span class="sd">Increments at some snapshot will be stored in ``Snapshot`` object.</span>
+
+<span class="sd">The input and result of power flow calculation are stored in the same</span>
+<span class="sd">instance. There are two kinds of results, voltages and flows.</span>
+<span class="sd">&quot;&quot;&quot;</span>
+<span class="kn">from</span> <span class="nn">typing</span> <span class="kn">import</span> <span class="n">List</span><span class="p">,</span> <span class="n">Union</span>
+
+<span class="kn">from</span> <span class="nn">pandas.core.series</span> <span class="kn">import</span> <span class="n">Series</span>
+
+
+<div class="viewcode-block" id="SnapshotSeries"><a class="viewcode-back" href="../../../snapshots.html#mgrid.power_flow.series.SnapshotSeries">[docs]</a><span class="k">class</span> <span class="nc">SnapshotSeries</span><span class="p">(</span><span class="nb">list</span><span class="p">):</span>
+
+<div class="viewcode-block" id="SnapshotSeries.add_series"><a class="viewcode-back" href="../../../snapshots.html#mgrid.power_flow.series.SnapshotSeries.add_series">[docs]</a>    <span class="k">def</span> <span class="nf">add_series</span><span class="p">(</span><span class="n">name</span><span class="p">:</span> <span class="nb">str</span><span class="p">,</span> <span class="n">attribute</span><span class="p">:</span> <span class="nb">str</span><span class="p">,</span> <span class="n">values</span><span class="p">:</span> <span class="n">Union</span><span class="p">[</span><span class="n">Series</span><span class="p">,</span> <span class="n">List</span><span class="p">]):</span>
+        <span class="k">pass</span></div>
+
+<div class="viewcode-block" id="SnapshotSeries.add_snapshot"><a class="viewcode-back" href="../../../snapshots.html#mgrid.power_flow.series.SnapshotSeries.add_snapshot">[docs]</a>    <span class="k">def</span> <span class="nf">add_snapshot</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">time</span><span class="p">:</span> <span class="nb">int</span><span class="p">):</span>
+        <span class="k">pass</span></div>
+
+<div class="viewcode-block" id="SnapshotSeries.get_series"><a class="viewcode-back" href="../../../snapshots.html#mgrid.power_flow.series.SnapshotSeries.get_series">[docs]</a>    <span class="k">def</span> <span class="nf">get_series</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
+        <span class="k">pass</span></div></div>
+</pre></div>
+
+           </div>
+
+          </div>
+          <footer>
+
+  <hr/>
+
+  <div role="contentinfo">
+    <p>
+        &#169; Copyright 2020-2021, Edward Xu.
+
+    </p>
+  </div>
+
+
+
+    Built with <a href="https://www.sphinx-doc.org/">Sphinx</a> using a
+
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+</html>
\ No newline at end of file
diff --git a/docs/_modules/mgrid/power_flow/snapshot.html b/docs/_modules/mgrid/power_flow/snapshot.html
new file mode 100644
index 0000000..7013b30
--- /dev/null
+++ b/docs/_modules/mgrid/power_flow/snapshot.html
@@ -0,0 +1,276 @@
+
+
+<!DOCTYPE html>
+<html class="writer-html5" lang="en" >
+<head>
+  <meta charset="utf-8" />
+
+  <meta name="viewport" content="width=device-width, initial-scale=1.0" />
+
+  <title>mgrid.power_flow.snapshot &mdash; mgrid v0.2.5 documentation</title>
+
+
+
+  <link rel="stylesheet" href="../../../_static/css/theme.css" type="text/css" />
+  <link rel="stylesheet" href="../../../_static/pygments.css" type="text/css" />
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+    <script src="../../../_static/js/html5shiv.min.js"></script>
+  <![endif]-->
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+        <script src="../../../_static/jquery.js"></script>
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+
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+  <div class="wy-grid-for-nav">
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+        <div class="wy-side-nav-search" >
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+    <a href="https://github.com/edxu96/mgrid/tree/main/docs_raw">documentation source</a> |
+    <a href="https://github.com/edxu96/mgrid">repository</a>
+
+
+
+            <a href="../../../index.html" class="icon icon-home"> mgrid
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+          </a>
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+  </form>
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+        <div class="wy-menu wy-menu-vertical" data-spy="affix" role="navigation" aria-label="main navigation">
+
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+              <ul>
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+<li class="toctree-l1"><a class="reference internal" href="../../../grid.html">Power Grid</a></li>
+<li class="toctree-l1"><a class="reference internal" href="../../../transformation.html">Transformation</a></li>
+<li class="toctree-l1"><a class="reference internal" href="../../../power_flow.html">Power Flow Calculation</a></li>
+<li class="toctree-l1"><a class="reference internal" href="../../../snapshots.html">Snapshot</a></li>
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+          <li><a href="../../index.html">Module code</a> &raquo;</li>
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+      <li>mgrid.power_flow.snapshot</li>
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+
+  <h1>Source code for mgrid.power_flow.snapshot</h1><div class="highlight"><pre>
+<span></span><span class="sd">&quot;&quot;&quot;Store input and calculation results in snapshots.</span>
+
+<span class="sd">Though the power system operates continuously, it is considered in</span>
+<span class="sd">discrete time in power flow calculation. That is, between two</span>
+<span class="sd">consecutive time indices, the system state is assumed to remain steady,</span>
+<span class="sd">so small variations are ignored. Usually, the duration between indices</span>
+<span class="sd">is long compared to the frequency of alternating current (50 Hz in</span>
+<span class="sd">Europe and 60 Hz in the US).</span>
+
+<span class="sd">The result for voltages in the previous snapshot can be used as the</span>
+<span class="sd">initial guess in power flow calculation.</span>
+<span class="sd">&quot;&quot;&quot;</span>
+<span class="kn">from</span> <span class="nn">__future__</span> <span class="kn">import</span> <span class="n">annotations</span>
+<span class="kn">from</span> <span class="nn">dataclasses</span> <span class="kn">import</span> <span class="n">dataclass</span>
+<span class="kn">from</span> <span class="nn">typing</span> <span class="kn">import</span> <span class="n">Dict</span><span class="p">,</span> <span class="n">Optional</span><span class="p">,</span> <span class="n">Tuple</span><span class="p">,</span> <span class="n">Union</span>
+
+<span class="kn">from</span> <span class="nn">pandas.core.frame</span> <span class="kn">import</span> <span class="n">DataFrame</span>
+
+<span class="kn">from</span> <span class="nn">mgrid.grid</span> <span class="kn">import</span> <span class="n">GeoGrid</span><span class="p">,</span> <span class="n">SupraGrid</span>
+
+
+<div class="viewcode-block" id="Snapshot"><a class="viewcode-back" href="../../../snapshots.html#mgrid.power_flow.snapshot.Snapshot">[docs]</a><span class="nd">@dataclass</span>
+<span class="k">class</span> <span class="nc">Snapshot</span><span class="p">:</span>
+    <span class="sd">&quot;&quot;&quot;Store input in incremental format and results in dataframes.&quot;&quot;&quot;</span>
+
+    <span class="c1">#: incremental values of conversion elements with respect to</span>
+    <span class="c1">#: the previous snapshot</span>
+    <span class="n">increments</span><span class="p">:</span> <span class="n">Dict</span><span class="p">[</span><span class="n">Tuple</span><span class="p">[</span><span class="nb">str</span><span class="p">,</span> <span class="nb">str</span><span class="p">],</span> <span class="nb">float</span><span class="p">]</span>
+    <span class="n">previous</span><span class="p">:</span> <span class="n">Union</span><span class="p">[</span><span class="n">GeoGrid</span><span class="p">,</span> <span class="n">Snapshot</span><span class="p">,</span> <span class="n">SupraGrid</span><span class="p">]</span>  <span class="c1">#: previous snapshot</span>
+    <span class="n">voltages</span><span class="p">:</span> <span class="n">Optional</span><span class="p">[</span><span class="n">DataFrame</span><span class="p">]</span> <span class="o">=</span> <span class="kc">None</span>  <span class="c1">#: votlage at buses in kVA</span>
+    <span class="n">flows</span><span class="p">:</span> <span class="n">Optional</span><span class="p">[</span><span class="n">DataFrame</span><span class="p">]</span> <span class="o">=</span> <span class="kc">None</span>  <span class="c1">#: power flow along edges in kW</span>
+
+<div class="viewcode-block" id="Snapshot.update_previsou"><a class="viewcode-back" href="../../../snapshots.html#mgrid.power_flow.snapshot.Snapshot.update_previsou">[docs]</a>    <span class="k">def</span> <span class="nf">update_previsou</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">previous</span><span class="p">:</span> <span class="n">Snapshot</span><span class="p">):</span>
+        <span class="sd">&quot;&quot;&quot;Update items with respect to given previous snapshost.</span>
+
+<span class="sd">        Args:</span>
+<span class="sd">            previous: another snapshot used as previous reference.</span>
+<span class="sd">        &quot;&quot;&quot;</span>
+        <span class="k">pass</span></div>
+
+    <span class="nd">@property</span>
+    <span class="k">def</span> <span class="nf">base</span><span class="p">(</span><span class="bp">self</span><span class="p">)</span> <span class="o">-&gt;</span> <span class="n">Union</span><span class="p">[</span><span class="n">GeoGrid</span><span class="p">,</span> <span class="n">SupraGrid</span><span class="p">]:</span>
+        <span class="sd">&quot;&quot;&quot;Get the base grid model and snapshot.</span>
+
+<span class="sd">        Returns:</span>
+<span class="sd">            [type]: [description]</span>
+<span class="sd">        &quot;&quot;&quot;</span>
+        <span class="n">pre</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">previous</span>
+        <span class="k">while</span> <span class="ow">not</span> <span class="p">(</span><span class="nb">isinstance</span><span class="p">(</span><span class="n">pre</span><span class="p">,</span> <span class="n">GeoGrid</span><span class="p">)</span> <span class="ow">or</span> <span class="nb">isinstance</span><span class="p">(</span><span class="n">pre</span><span class="p">,</span> <span class="n">SupraGrid</span><span class="p">)):</span>
+            <span class="n">pre</span> <span class="o">=</span> <span class="n">pre</span><span class="o">.</span><span class="n">previous</span>
+        <span class="k">return</span> <span class="n">pre</span>
+
+<div class="viewcode-block" id="Snapshot.result_pandapower"><a class="viewcode-back" href="../../../snapshots.html#mgrid.power_flow.snapshot.Snapshot.result_pandapower">[docs]</a>    <span class="k">def</span> <span class="nf">result_pandapower</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">net</span><span class="p">):</span>
+        <span class="sd">&quot;&quot;&quot;Get results from a ``pandapower`` model.</span>
+
+<span class="sd">        Args:</span>
+<span class="sd">            net: a grid modelled using ``pandapower``.</span>
+<span class="sd">        &quot;&quot;&quot;</span>
+        <span class="k">pass</span></div>
+
+<div class="viewcode-block" id="Snapshot.result_pypsa"><a class="viewcode-back" href="../../../snapshots.html#mgrid.power_flow.snapshot.Snapshot.result_pypsa">[docs]</a>    <span class="k">def</span> <span class="nf">result_pypsa</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">net</span><span class="p">):</span>
+        <span class="sd">&quot;&quot;&quot;Get results from a ``pypsa`` model.</span>
+
+<span class="sd">        Args:</span>
+<span class="sd">            net: a grid modelled using ``pypsa``.</span>
+<span class="sd">        &quot;&quot;&quot;</span>
+        <span class="k">pass</span></div></div>
+</pre></div>
+
+           </div>
+
+          </div>
+          <footer>
+
+  <hr/>
+
+  <div role="contentinfo">
+    <p>
+        &#169; Copyright 2020-2021, Edward Xu.
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diff --git a/docs/_modules/mgrid/power_flow/type.html b/docs/_modules/mgrid/power_flow/type.html
index 95c849c..2fe853e 100644
--- a/docs/_modules/mgrid/power_flow/type.html
+++ b/docs/_modules/mgrid/power_flow/type.html
@@ -89,8 +89,9 @@
               <ul>
 <li class="toctree-l1"><a class="reference internal" href="../../../graph.html">Graph Theoretic Model</a></li>
 <li class="toctree-l1"><a class="reference internal" href="../../../grid.html">Power Grid</a></li>
-<li class="toctree-l1"><a class="reference internal" href="../../../power_flow.html">Power Flow Calculation</a></li>
 <li class="toctree-l1"><a class="reference internal" href="../../../transformation.html">Transformation</a></li>
+<li class="toctree-l1"><a class="reference internal" href="../../../power_flow.html">Power Flow Calculation</a></li>
+<li class="toctree-l1"><a class="reference internal" href="../../../snapshots.html">Snapshot</a></li>
 </ul>
 <ul>
 <li class="toctree-l1"><a class="reference internal" href="../../../bibliography.html">Bibliography</a></li>
diff --git a/docs/_modules/mgrid/transformation.html b/docs/_modules/mgrid/transformation.html
index 6fef32b..cfaa474 100644
--- a/docs/_modules/mgrid/transformation.html
+++ b/docs/_modules/mgrid/transformation.html
@@ -89,8 +89,9 @@
               <ul>
 <li class="toctree-l1"><a class="reference internal" href="../../graph.html">Graph Theoretic Model</a></li>
 <li class="toctree-l1"><a class="reference internal" href="../../grid.html">Power Grid</a></li>
-<li class="toctree-l1"><a class="reference internal" href="../../power_flow.html">Power Flow Calculation</a></li>
 <li class="toctree-l1"><a class="reference internal" href="../../transformation.html">Transformation</a></li>
+<li class="toctree-l1"><a class="reference internal" href="../../power_flow.html">Power Flow Calculation</a></li>
+<li class="toctree-l1"><a class="reference internal" href="../../snapshots.html">Snapshot</a></li>
 </ul>
 <ul>
 <li class="toctree-l1"><a class="reference internal" href="../../bibliography.html">Bibliography</a></li>
@@ -160,23 +161,23 @@
            <div itemprop="articleBody">
 
   <h1>Source code for mgrid.transformation</h1><div class="highlight"><pre>
-<span></span><span class="sd">&quot;&quot;&quot;Function to transform multilayer network from one format to another.&quot;&quot;&quot;</span>
+<span></span><span class="sd">&quot;&quot;&quot;Function to convert planar graph to supra graph.&quot;&quot;&quot;</span>
 <span class="kn">from</span> <span class="nn">copy</span> <span class="kn">import</span> <span class="n">deepcopy</span>
 <span class="kn">from</span> <span class="nn">itertools</span> <span class="kn">import</span> <span class="n">chain</span>
 <span class="kn">from</span> <span class="nn">statistics</span> <span class="kn">import</span> <span class="n">mean</span>
-<span class="kn">from</span> <span class="nn">typing</span> <span class="kn">import</span> <span class="n">Tuple</span><span class="p">,</span> <span class="n">Union</span>
+<span class="kn">from</span> <span class="nn">typing</span> <span class="kn">import</span> <span class="n">Dict</span><span class="p">,</span> <span class="n">Set</span><span class="p">,</span> <span class="n">Tuple</span><span class="p">,</span> <span class="n">Union</span>
 
 <span class="kn">import</span> <span class="nn">networkx</span> <span class="k">as</span> <span class="nn">nx</span>
 <span class="kn">import</span> <span class="nn">pandas</span> <span class="k">as</span> <span class="nn">pd</span>
 
-<span class="kn">from</span> <span class="nn">mgrid.graph.planar</span> <span class="kn">import</span> <span class="n">COLUMNS</span><span class="p">,</span> <span class="n">COLUMNS_DI</span><span class="p">,</span> <span class="n">PlanarGraph</span>
-<span class="kn">from</span> <span class="nn">mgrid.grid</span> <span class="kn">import</span> <span class="n">PlanarGrid</span><span class="p">,</span> <span class="n">SupraGrid</span>
+<span class="kn">from</span> <span class="nn">mgrid.graph.geographic</span> <span class="kn">import</span> <span class="n">COLUMNS</span><span class="p">,</span> <span class="n">COLUMNS_DI</span><span class="p">,</span> <span class="n">GeoGraph</span>
+<span class="kn">from</span> <span class="nn">mgrid.grid</span> <span class="kn">import</span> <span class="n">GeoGrid</span><span class="p">,</span> <span class="n">SupraGrid</span>
 <span class="kn">from</span> <span class="nn">mgrid.log</span> <span class="kn">import</span> <span class="n">LOGGER</span>
 
 <span class="n">COLUMNS_DI_ORIGINAL</span> <span class="o">=</span> <span class="p">[</span><span class="s2">&quot;source_original&quot;</span><span class="p">,</span> <span class="s2">&quot;target_original&quot;</span><span class="p">]</span>
 
 
-<span class="k">def</span> <span class="nf">_planar2supra</span><span class="p">(</span><span class="n">g</span><span class="p">:</span> <span class="n">PlanarGrid</span><span class="p">)</span> <span class="o">-&gt;</span> <span class="n">SupraGrid</span><span class="p">:</span>
+<span class="k">def</span> <span class="nf">_planar2supra</span><span class="p">(</span><span class="n">g</span><span class="p">:</span> <span class="n">GeoGrid</span><span class="p">)</span> <span class="o">-&gt;</span> <span class="n">Tuple</span><span class="p">[</span><span class="n">SupraGrid</span><span class="p">,</span> <span class="n">Dict</span><span class="p">[</span><span class="nb">int</span><span class="p">,</span> <span class="n">Set</span><span class="p">[</span><span class="nb">str</span><span class="p">]]]:</span>
     <span class="sd">&quot;&quot;&quot;Convert a planar grid to corresponding supra-grid.</span>
 
 <span class="sd">    Args:</span>
@@ -251,14 +252,13 @@ <h1>Source code for mgrid.transformation</h1><div class="highlight"><pre>
         <span class="n">target</span> <span class="o">=</span> <span class="n">init_node4inter</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
         <span class="n">dg</span><span class="o">.</span><span class="n">add_edge</span><span class="p">(</span><span class="n">source</span><span class="p">,</span> <span class="n">target</span><span class="p">,</span> <span class="n">layer</span><span class="o">=</span><span class="n">mean</span><span class="p">([</span><span class="n">row</span><span class="p">[</span><span class="s2">&quot;upper&quot;</span><span class="p">],</span> <span class="n">row</span><span class="p">[</span><span class="s2">&quot;lower&quot;</span><span class="p">]]))</span>
 
-        <span class="n">dg</span><span class="o">.</span><span class="n">remove_node</span><span class="p">(</span><span class="n">node</span><span class="p">)</span>
+        <span class="c1"># Store layer and origin of inter-edge terminals as node attributes</span>
+        <span class="n">dg</span><span class="o">.</span><span class="n">nodes</span><span class="p">[</span><span class="n">source</span><span class="p">][</span><span class="s2">&quot;layer&quot;</span><span class="p">]</span> <span class="o">=</span> <span class="n">row</span><span class="p">[</span><span class="s2">&quot;upper&quot;</span><span class="p">]</span>
+        <span class="n">dg</span><span class="o">.</span><span class="n">nodes</span><span class="p">[</span><span class="n">source</span><span class="p">][</span><span class="s2">&quot;origin&quot;</span><span class="p">]</span> <span class="o">=</span> <span class="n">node</span>
+        <span class="n">dg</span><span class="o">.</span><span class="n">nodes</span><span class="p">[</span><span class="n">target</span><span class="p">][</span><span class="s2">&quot;layer&quot;</span><span class="p">]</span> <span class="o">=</span> <span class="n">row</span><span class="p">[</span><span class="s2">&quot;lower&quot;</span><span class="p">]</span>
+        <span class="n">dg</span><span class="o">.</span><span class="n">nodes</span><span class="p">[</span><span class="n">target</span><span class="p">][</span><span class="s2">&quot;origin&quot;</span><span class="p">]</span> <span class="o">=</span> <span class="n">node</span>
 
-    <span class="c1"># Build nodelist using dictionary for nodes in different layers.</span>
-    <span class="n">keys_sorted</span> <span class="o">=</span> <span class="nb">sorted</span><span class="p">(</span><span class="n">node_dict</span><span class="p">)</span>
-    <span class="n">nodelist</span> <span class="o">=</span> <span class="n">pd</span><span class="o">.</span><span class="n">DataFrame</span><span class="p">(</span>
-        <span class="p">{</span><span class="s2">&quot;idx&quot;</span><span class="p">:</span> <span class="n">chain</span><span class="p">(</span><span class="o">*</span><span class="p">[[</span><span class="n">key</span><span class="p">]</span> <span class="o">*</span> <span class="nb">len</span><span class="p">(</span><span class="n">node_dict</span><span class="p">[</span><span class="n">key</span><span class="p">])</span> <span class="k">for</span> <span class="n">key</span> <span class="ow">in</span> <span class="n">keys_sorted</span><span class="p">])},</span>
-        <span class="n">index</span><span class="o">=</span><span class="n">chain</span><span class="p">(</span><span class="o">*</span><span class="p">[</span><span class="n">node_dict</span><span class="p">[</span><span class="n">key</span><span class="p">]</span> <span class="k">for</span> <span class="n">key</span> <span class="ow">in</span> <span class="n">keys_sorted</span><span class="p">]),</span>
-    <span class="p">)</span>
+        <span class="n">dg</span><span class="o">.</span><span class="n">remove_node</span><span class="p">(</span><span class="n">node</span><span class="p">)</span>
 
     <span class="c1"># Build supra-grid.</span>
     <span class="n">res</span> <span class="o">=</span> <span class="n">SupraGrid</span><span class="p">(</span><span class="n">dg</span><span class="p">)</span>
@@ -267,14 +267,10 @@ <h1>Source code for mgrid.transformation</h1><div class="highlight"><pre>
     <span class="n">res</span><span class="o">.</span><span class="n">inter_edges</span><span class="o">.</span><span class="n">index</span><span class="o">.</span><span class="n">name</span> <span class="o">=</span> <span class="s2">&quot;node&quot;</span>
 
     <span class="n">res</span><span class="o">.</span><span class="n">df_layers</span> <span class="o">=</span> <span class="n">g</span><span class="o">.</span><span class="n">df_layers</span><span class="o">.</span><span class="n">copy</span><span class="p">(</span><span class="n">deep</span><span class="o">=</span><span class="kc">True</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">res</span><span class="p">,</span> <span class="n">node_dict</span>
 
-    <span class="n">res</span><span class="o">.</span><span class="n">nodelist</span> <span class="o">=</span> <span class="n">nodelist</span>
-    <span class="n">res</span><span class="o">.</span><span class="n">nodelist</span><span class="p">[</span><span class="s2">&quot;name&quot;</span><span class="p">]</span> <span class="o">=</span> <span class="n">res</span><span class="o">.</span><span class="n">nodelist</span><span class="p">[</span><span class="s2">&quot;idx&quot;</span><span class="p">]</span><span class="o">.</span><span class="n">map</span><span class="p">(</span><span class="n">res</span><span class="o">.</span><span class="n">df_layers</span><span class="p">[</span><span class="s2">&quot;name&quot;</span><span class="p">])</span>
-    <span class="n">res</span><span class="o">.</span><span class="n">nodelist</span><span class="o">.</span><span class="n">index</span><span class="o">.</span><span class="n">name</span> <span class="o">=</span> <span class="s2">&quot;node&quot;</span>
-    <span class="k">return</span> <span class="n">res</span>
 
-
-<div class="viewcode-block" id="planar2supra"><a class="viewcode-back" href="../../transformation.html#mgrid.transformation.planar2supra">[docs]</a><span class="k">def</span> <span class="nf">planar2supra</span><span class="p">(</span><span class="n">g</span><span class="p">:</span> <span class="n">Union</span><span class="p">[</span><span class="n">PlanarGraph</span><span class="p">,</span> <span class="n">PlanarGrid</span><span class="p">])</span> <span class="o">-&gt;</span> <span class="n">SupraGrid</span><span class="p">:</span>
+<div class="viewcode-block" id="planar2supra"><a class="viewcode-back" href="../../transformation.html#mgrid.transformation.planar2supra">[docs]</a><span class="k">def</span> <span class="nf">planar2supra</span><span class="p">(</span><span class="n">g</span><span class="p">:</span> <span class="n">Union</span><span class="p">[</span><span class="n">GeoGraph</span><span class="p">,</span> <span class="n">GeoGrid</span><span class="p">])</span> <span class="o">-&gt;</span> <span class="n">SupraGrid</span><span class="p">:</span>
     <span class="sd">&quot;&quot;&quot;Convert a planar grid to corresponding supra-grid.</span>
 
 <span class="sd">    Args:</span>
@@ -284,21 +280,45 @@ <h1>Source code for mgrid.transformation</h1><div class="highlight"><pre>
 <span class="sd">        Resulted supra graph (for the grid).</span>
 
 <span class="sd">    &quot;&quot;&quot;</span>
-    <span class="n">supra</span> <span class="o">=</span> <span class="n">_planar2supra</span><span class="p">(</span><span class="n">g</span><span class="p">)</span>
+    <span class="n">supra</span><span class="p">,</span> <span class="n">node_dict</span> <span class="o">=</span> <span class="n">_planar2supra</span><span class="p">(</span><span class="n">g</span><span class="p">)</span>
 
-    <span class="k">if</span> <span class="nb">isinstance</span><span class="p">(</span><span class="n">g</span><span class="p">,</span> <span class="n">PlanarGrid</span><span class="p">):</span>
+    <span class="k">if</span> <span class="nb">isinstance</span><span class="p">(</span><span class="n">g</span><span class="p">,</span> <span class="n">GeoGrid</span><span class="p">):</span>
         <span class="k">for</span> <span class="n">node</span><span class="p">,</span> <span class="n">row</span> <span class="ow">in</span> <span class="n">g</span><span class="o">.</span><span class="n">inter_nodes</span><span class="o">.</span><span class="n">iterrows</span><span class="p">():</span>
             <span class="n">source</span> <span class="o">=</span> <span class="n">supra</span><span class="o">.</span><span class="n">inter_edges</span><span class="o">.</span><span class="n">loc</span><span class="p">[</span><span class="n">node</span><span class="p">,</span> <span class="s2">&quot;source&quot;</span><span class="p">]</span>
             <span class="n">target</span> <span class="o">=</span> <span class="n">supra</span><span class="o">.</span><span class="n">inter_edges</span><span class="o">.</span><span class="n">loc</span><span class="p">[</span><span class="n">node</span><span class="p">,</span> <span class="s2">&quot;target&quot;</span><span class="p">]</span>
             <span class="n">supra</span><span class="o">.</span><span class="n">edges</span><span class="p">[</span><span class="n">source</span><span class="p">,</span> <span class="n">target</span><span class="p">][</span><span class="s2">&quot;element&quot;</span><span class="p">]</span> <span class="o">=</span> <span class="n">row</span><span class="p">[</span><span class="s2">&quot;element&quot;</span><span class="p">]</span>
 
-        <span class="n">supra</span><span class="o">.</span><span class="n">conversions</span> <span class="o">=</span> <span class="n">deepcopy</span><span class="p">(</span><span class="n">g</span><span class="o">.</span><span class="n">conversions</span><span class="p">)</span>
+        <span class="c1"># Get conversion elements.</span>
+        <span class="n">conversions</span> <span class="o">=</span> <span class="n">deepcopy</span><span class="p">(</span><span class="n">g</span><span class="o">.</span><span class="n">conversions</span><span class="p">)</span>
+        <span class="n">conversions</span><span class="o">.</span><span class="n">reset_index</span><span class="p">(</span><span class="n">inplace</span><span class="o">=</span><span class="kc">True</span><span class="p">)</span>
+        <span class="n">conversions</span> <span class="o">=</span> <span class="n">pd</span><span class="o">.</span><span class="n">merge</span><span class="p">(</span>
+            <span class="n">conversions</span><span class="p">,</span>
+            <span class="n">supra</span><span class="o">.</span><span class="n">nodes_new</span><span class="p">,</span>
+            <span class="n">how</span><span class="o">=</span><span class="s2">&quot;left&quot;</span><span class="p">,</span>
+            <span class="n">left_on</span><span class="o">=</span><span class="p">[</span><span class="s2">&quot;node&quot;</span><span class="p">,</span> <span class="s2">&quot;layer&quot;</span><span class="p">],</span>
+            <span class="n">right_index</span><span class="o">=</span><span class="kc">True</span><span class="p">,</span>
+        <span class="p">)</span>
+        <span class="n">conversions</span><span class="o">.</span><span class="n">set_index</span><span class="p">(</span><span class="s2">&quot;name&quot;</span><span class="p">,</span> <span class="n">inplace</span><span class="o">=</span><span class="kc">True</span><span class="p">)</span>
+        <span class="n">conversions</span><span class="o">.</span><span class="n">drop</span><span class="p">(</span><span class="n">columns</span><span class="o">=</span><span class="p">[</span><span class="s2">&quot;node&quot;</span><span class="p">,</span> <span class="s2">&quot;layer&quot;</span><span class="p">],</span> <span class="n">inplace</span><span class="o">=</span><span class="kc">True</span><span class="p">)</span>
+        <span class="n">supra</span><span class="o">.</span><span class="n">conversions</span> <span class="o">=</span> <span class="n">conversions</span>
+
         <span class="n">supra</span><span class="o">.</span><span class="n">types</span> <span class="o">=</span> <span class="n">deepcopy</span><span class="p">(</span><span class="n">g</span><span class="o">.</span><span class="n">types</span><span class="p">)</span>
 
-        <span class="n">supra</span><span class="o">.</span><span class="n">nodelist</span><span class="p">[</span><span class="s2">&quot;voltage&quot;</span><span class="p">]</span> <span class="o">=</span> <span class="n">supra</span><span class="o">.</span><span class="n">nodelist</span><span class="p">[</span><span class="s2">&quot;idx&quot;</span><span class="p">]</span><span class="o">.</span><span class="n">map</span><span class="p">(</span>
-            <span class="n">supra</span><span class="o">.</span><span class="n">df_layers</span><span class="p">[</span><span class="s2">&quot;voltage&quot;</span><span class="p">]</span>
+        <span class="c1"># Build a list of buses using dictionary for nodes in different layers.</span>
+        <span class="n">keys_sorted</span> <span class="o">=</span> <span class="nb">sorted</span><span class="p">(</span><span class="n">node_dict</span><span class="p">)</span>
+        <span class="n">data</span> <span class="o">=</span> <span class="p">{</span>
+            <span class="s2">&quot;idx&quot;</span><span class="p">:</span> <span class="n">chain</span><span class="p">(</span><span class="o">*</span><span class="p">[[</span><span class="n">key</span><span class="p">]</span> <span class="o">*</span> <span class="nb">len</span><span class="p">(</span><span class="n">node_dict</span><span class="p">[</span><span class="n">key</span><span class="p">])</span> <span class="k">for</span> <span class="n">key</span> <span class="ow">in</span> <span class="n">keys_sorted</span><span class="p">])</span>
+        <span class="p">}</span>
+        <span class="n">buses</span> <span class="o">=</span> <span class="n">pd</span><span class="o">.</span><span class="n">DataFrame</span><span class="p">(</span>
+            <span class="n">data</span><span class="p">,</span>
+            <span class="n">index</span><span class="o">=</span><span class="n">chain</span><span class="p">(</span><span class="o">*</span><span class="p">[</span><span class="n">node_dict</span><span class="p">[</span><span class="n">key</span><span class="p">]</span> <span class="k">for</span> <span class="n">key</span> <span class="ow">in</span> <span class="n">keys_sorted</span><span class="p">]),</span>
         <span class="p">)</span>
 
+        <span class="n">buses</span><span class="p">[</span><span class="s2">&quot;layer_name&quot;</span><span class="p">]</span> <span class="o">=</span> <span class="n">buses</span><span class="p">[</span><span class="s2">&quot;idx&quot;</span><span class="p">]</span><span class="o">.</span><span class="n">map</span><span class="p">(</span><span class="n">supra</span><span class="o">.</span><span class="n">df_layers</span><span class="p">[</span><span class="s2">&quot;name&quot;</span><span class="p">])</span>
+        <span class="n">buses</span><span class="o">.</span><span class="n">index</span><span class="o">.</span><span class="n">name</span> <span class="o">=</span> <span class="s2">&quot;node&quot;</span>
+        <span class="n">buses</span><span class="p">[</span><span class="s2">&quot;voltage&quot;</span><span class="p">]</span> <span class="o">=</span> <span class="n">buses</span><span class="p">[</span><span class="s2">&quot;idx&quot;</span><span class="p">]</span><span class="o">.</span><span class="n">map</span><span class="p">(</span><span class="n">supra</span><span class="o">.</span><span class="n">df_layers</span><span class="p">[</span><span class="s2">&quot;voltage&quot;</span><span class="p">])</span>
+        <span class="n">supra</span><span class="o">.</span><span class="n">buses</span> <span class="o">=</span> <span class="n">buses</span>
+
     <span class="k">return</span> <span class="n">supra</span></div>
 </pre></div>
 
diff --git a/docs/_sources/graph.rst.txt b/docs/_sources/graph.rst.txt
index c7c56a5..7587fb4 100644
--- a/docs/_sources/graph.rst.txt
+++ b/docs/_sources/graph.rst.txt
@@ -1,10 +1,10 @@
 Graph Theoretic Model
 =====================
 
-Planar Graph
-------------
+Geographic Graph
+----------------
 
-.. automodule:: mgrid.graph.planar
+.. automodule:: mgrid.graph.geographic
    :members:
    :undoc-members:
    :show-inheritance:
diff --git a/docs/_sources/grid.rst.txt b/docs/_sources/grid.rst.txt
index 1283b05..43c99e2 100644
--- a/docs/_sources/grid.rst.txt
+++ b/docs/_sources/grid.rst.txt
@@ -1,10 +1,10 @@
 Power Grid
 ==========
 
-as Planar Graph
----------------
+as Geographic Graph
+-------------------
 
-.. automodule:: mgrid.grid.planar
+.. automodule:: mgrid.grid.geographic
    :members:
    :undoc-members:
    :show-inheritance:
diff --git a/docs/_sources/index.rst.txt b/docs/_sources/index.rst.txt
index 069e437..fdca045 100644
--- a/docs/_sources/index.rst.txt
+++ b/docs/_sources/index.rst.txt
@@ -112,8 +112,9 @@ API
 
    graph
    grid
-   power_flow
    transformation
+   power_flow
+   snapshots
 
 Bibliography
 ------------
diff --git a/docs/_sources/snapshots.rst.txt b/docs/_sources/snapshots.rst.txt
new file mode 100644
index 0000000..79acb2e
--- /dev/null
+++ b/docs/_sources/snapshots.rst.txt
@@ -0,0 +1,15 @@
+Snapshot
+========
+
+.. automodule:: mgrid.power_flow.snapshot
+   :members:
+   :undoc-members:
+   :show-inheritance:
+
+Snapshot Series
+---------------
+
+.. automodule:: mgrid.power_flow.series
+   :members:
+   :undoc-members:
+   :show-inheritance:
diff --git a/docs/bibliography.html b/docs/bibliography.html
index 9d78f69..bdbb34c 100644
--- a/docs/bibliography.html
+++ b/docs/bibliography.html
@@ -38,7 +38,7 @@
 
     <link rel="index" title="Index" href="genindex.html" />
     <link rel="search" title="Search" href="search.html" />
-    <link rel="prev" title="Transformation" href="transformation.html" />
+    <link rel="prev" title="Snapshot" href="snapshots.html" />
 </head>
 
 <body class="wy-body-for-nav">
@@ -90,8 +90,9 @@
               <ul>
 <li class="toctree-l1"><a class="reference internal" href="graph.html">Graph Theoretic Model</a></li>
 <li class="toctree-l1"><a class="reference internal" href="grid.html">Power Grid</a></li>
-<li class="toctree-l1"><a class="reference internal" href="power_flow.html">Power Flow Calculation</a></li>
 <li class="toctree-l1"><a class="reference internal" href="transformation.html">Transformation</a></li>
+<li class="toctree-l1"><a class="reference internal" href="power_flow.html">Power Flow Calculation</a></li>
+<li class="toctree-l1"><a class="reference internal" href="snapshots.html">Snapshot</a></li>
 </ul>
 <ul class="current">
 <li class="toctree-l1 current"><a class="current reference internal" href="#">Bibliography</a></li>
@@ -192,7 +193,7 @@ <h1>Bibliography<a class="headerlink" href="#bibliography" title="Permalink to t
           </div>
           <footer>
     <div class="rst-footer-buttons" role="navigation" aria-label="footer navigation">
-        <a href="transformation.html" class="btn btn-neutral float-left" title="Transformation" accesskey="p" rel="prev"><span class="fa fa-arrow-circle-left" aria-hidden="true"></span> Previous</a>
+        <a href="snapshots.html" class="btn btn-neutral float-left" title="Snapshot" accesskey="p" rel="prev"><span class="fa fa-arrow-circle-left" aria-hidden="true"></span> Previous</a>
     </div>
 
   <hr/>
diff --git a/docs/genindex.html b/docs/genindex.html
index 56b9074..63d7ed3 100644
--- a/docs/genindex.html
+++ b/docs/genindex.html
@@ -89,8 +89,9 @@
               <ul>
 <li class="toctree-l1"><a class="reference internal" href="graph.html">Graph Theoretic Model</a></li>
 <li class="toctree-l1"><a class="reference internal" href="grid.html">Power Grid</a></li>
-<li class="toctree-l1"><a class="reference internal" href="power_flow.html">Power Flow Calculation</a></li>
 <li class="toctree-l1"><a class="reference internal" href="transformation.html">Transformation</a></li>
+<li class="toctree-l1"><a class="reference internal" href="power_flow.html">Power Flow Calculation</a></li>
+<li class="toctree-l1"><a class="reference internal" href="snapshots.html">Snapshot</a></li>
 </ul>
 <ul>
 <li class="toctree-l1"><a class="reference internal" href="bibliography.html">Bibliography</a></li>
@@ -165,10 +166,12 @@ <h1 id="index">Index</h1>
 <div class="genindex-jumpbox">
  <a href="#_"><strong>_</strong></a>
  | <a href="#A"><strong>A</strong></a>
+ | <a href="#B"><strong>B</strong></a>
  | <a href="#C"><strong>C</strong></a>
  | <a href="#D"><strong>D</strong></a>
  | <a href="#E"><strong>E</strong></a>
  | <a href="#F"><strong>F</strong></a>
+ | <a href="#G"><strong>G</strong></a>
  | <a href="#I"><strong>I</strong></a>
  | <a href="#L"><strong>L</strong></a>
  | <a href="#M"><strong>M</strong></a>
@@ -187,12 +190,12 @@ <h1 id="index">Index</h1>
 <h2 id="_">_</h2>
 <table style="width: 100%" class="indextable genindextable"><tr>
   <td style="width: 33%; vertical-align: top;"><ul>
-      <li><a href="graph.html#mgrid.graph.planar.PlanarGraph.__init__">__init__() (mgrid.graph.planar.PlanarGraph method)</a>
+      <li><a href="graph.html#mgrid.graph.geographic.GeoGraph.__init__">__init__() (mgrid.graph.geographic.GeoGraph method)</a>
 
       <ul>
         <li><a href="graph.html#mgrid.graph.supra.SupraGraph.__init__">(mgrid.graph.supra.SupraGraph method)</a>
 </li>
-        <li><a href="grid.html#mgrid.grid.planar.PlanarGrid.__init__">(mgrid.grid.planar.PlanarGrid method)</a>
+        <li><a href="grid.html#mgrid.grid.geographic.GeoGrid.__init__">(mgrid.grid.geographic.GeoGrid method)</a>
 </li>
         <li><a href="grid.html#mgrid.grid.supra.SupraGrid.__init__">(mgrid.grid.supra.SupraGrid method)</a>
 </li>
@@ -203,17 +206,33 @@ <h2 id="_">_</h2>
 <h2 id="A">A</h2>
 <table style="width: 100%" class="indextable genindextable"><tr>
   <td style="width: 33%; vertical-align: top;"><ul>
-      <li><a href="grid.html#mgrid.grid.planar.PlanarGrid.add_conversion">add_conversion() (mgrid.grid.planar.PlanarGrid method)</a>
+      <li><a href="grid.html#mgrid.grid.geographic.GeoGrid.add_conversion">add_conversion() (mgrid.grid.geographic.GeoGrid method)</a>
 </li>
-  </ul></td>
-  <td style="width: 33%; vertical-align: top;"><ul>
-      <li><a href="graph.html#mgrid.graph.planar.PlanarGraph.add_inter_node">add_inter_node() (mgrid.graph.planar.PlanarGraph method)</a>
+      <li><a href="graph.html#mgrid.graph.geographic.GeoGraph.add_inter_node">add_inter_node() (mgrid.graph.geographic.GeoGraph method)</a>
 
       <ul>
-        <li><a href="grid.html#mgrid.grid.planar.PlanarGrid.add_inter_node">(mgrid.grid.planar.PlanarGrid method)</a>
+        <li><a href="grid.html#mgrid.grid.geographic.GeoGrid.add_inter_node">(mgrid.grid.geographic.GeoGrid method)</a>
 </li>
       </ul></li>
   </ul></td>
+  <td style="width: 33%; vertical-align: top;"><ul>
+      <li><a href="snapshots.html#mgrid.power_flow.series.SnapshotSeries.add_series">add_series() (mgrid.power_flow.series.SnapshotSeries method)</a>
+</li>
+      <li><a href="snapshots.html#mgrid.power_flow.series.SnapshotSeries.add_snapshot">add_snapshot() (mgrid.power_flow.series.SnapshotSeries method)</a>
+</li>
+  </ul></td>
+</tr></table>
+
+<h2 id="B">B</h2>
+<table style="width: 100%" class="indextable genindextable"><tr>
+  <td style="width: 33%; vertical-align: top;"><ul>
+      <li><a href="snapshots.html#mgrid.power_flow.snapshot.Snapshot.base">base() (mgrid.power_flow.snapshot.Snapshot property)</a>
+</li>
+  </ul></td>
+  <td style="width: 33%; vertical-align: top;"><ul>
+      <li><a href="grid.html#mgrid.grid.supra.SupraGrid.buses">buses (mgrid.grid.supra.SupraGrid attribute)</a>
+</li>
+  </ul></td>
 </tr></table>
 
 <h2 id="C">C</h2>
@@ -233,20 +252,22 @@ <h2 id="C">C</h2>
 </li>
       <li><a href="power_flow.html#mgrid.power_flow.conversion.Capacitor">Capacitor (class in mgrid.power_flow.conversion)</a>
 </li>
-      <li><a href="grid.html#mgrid.grid.planar.PlanarGrid.conversion">conversion (mgrid.grid.planar.PlanarGrid attribute)</a>
-</li>
-      <li><a href="grid.html#mgrid.grid.supra.SupraGrid.conversions">conversions (mgrid.grid.supra.SupraGrid attribute)</a>
+      <li><a href="grid.html#mgrid.grid.geographic.GeoGrid.conversions">conversions (mgrid.grid.geographic.GeoGrid attribute)</a>
+
+      <ul>
+        <li><a href="grid.html#mgrid.grid.supra.SupraGrid.conversions">(mgrid.grid.supra.SupraGrid attribute)</a>
 </li>
+      </ul></li>
   </ul></td>
 </tr></table>
 
 <h2 id="D">D</h2>
 <table style="width: 100%" class="indextable genindextable"><tr>
   <td style="width: 33%; vertical-align: top;"><ul>
-      <li><a href="graph.html#mgrid.graph.planar.PlanarGraph.df_layers">df_layers (mgrid.graph.planar.PlanarGraph attribute)</a>
+      <li><a href="graph.html#mgrid.graph.geographic.GeoGraph.df_layers">df_layers (mgrid.graph.geographic.GeoGraph attribute)</a>
 
       <ul>
-        <li><a href="grid.html#mgrid.grid.planar.PlanarGrid.df_layers">(mgrid.grid.planar.PlanarGrid attribute)</a>
+        <li><a href="grid.html#mgrid.grid.geographic.GeoGrid.df_layers">(mgrid.grid.geographic.GeoGrid attribute)</a>
 </li>
       </ul></li>
   </ul></td>
@@ -263,11 +284,27 @@ <h2 id="E">E</h2>
 <h2 id="F">F</h2>
 <table style="width: 100%" class="indextable genindextable"><tr>
   <td style="width: 33%; vertical-align: top;"><ul>
-      <li><a href="graph.html#mgrid.graph.planar.PlanarGraph.find_layer">find_layer() (mgrid.graph.planar.PlanarGraph method)</a>
+      <li><a href="graph.html#mgrid.graph.geographic.GeoGraph.find_layer">find_layer() (mgrid.graph.geographic.GeoGraph method)</a>
+</li>
+  </ul></td>
+  <td style="width: 33%; vertical-align: top;"><ul>
+      <li><a href="snapshots.html#mgrid.power_flow.snapshot.Snapshot.flows">flows (mgrid.power_flow.snapshot.Snapshot attribute)</a>
+</li>
+      <li><a href="graph.html#mgrid.graph.geographic.GeoGraph.from_edgelist">from_edgelist() (mgrid.graph.geographic.GeoGraph class method)</a>
+</li>
+  </ul></td>
+</tr></table>
+
+<h2 id="G">G</h2>
+<table style="width: 100%" class="indextable genindextable"><tr>
+  <td style="width: 33%; vertical-align: top;"><ul>
+      <li><a href="graph.html#mgrid.graph.geographic.GeoGraph">GeoGraph (class in mgrid.graph.geographic)</a>
 </li>
   </ul></td>
   <td style="width: 33%; vertical-align: top;"><ul>
-      <li><a href="graph.html#mgrid.graph.planar.PlanarGraph.from_edgelist">from_edgelist() (mgrid.graph.planar.PlanarGraph class method)</a>
+      <li><a href="grid.html#mgrid.grid.geographic.GeoGrid">GeoGrid (class in mgrid.grid.geographic)</a>
+</li>
+      <li><a href="snapshots.html#mgrid.power_flow.series.SnapshotSeries.get_series">get_series() (mgrid.power_flow.series.SnapshotSeries method)</a>
 </li>
   </ul></td>
 </tr></table>
@@ -276,20 +313,22 @@ <h2 id="I">I</h2>
 <table style="width: 100%" class="indextable genindextable"><tr>
   <td style="width: 33%; vertical-align: top;"><ul>
       <li><a href="power_flow.html#mgrid.power_flow.type.TransformerType.i0_percent">i0_percent (mgrid.power_flow.type.TransformerType attribute)</a>
+</li>
+      <li><a href="snapshots.html#mgrid.power_flow.snapshot.Snapshot.increments">increments (mgrid.power_flow.snapshot.Snapshot attribute)</a>
 </li>
       <li><a href="graph.html#mgrid.graph.supra.SupraGraph.inter_edges">inter_edges (mgrid.graph.supra.SupraGraph attribute)</a>
 </li>
-      <li><a href="graph.html#mgrid.graph.planar.PlanarGraph.inter_nodes">inter_nodes (mgrid.graph.planar.PlanarGraph attribute)</a>
+  </ul></td>
+  <td style="width: 33%; vertical-align: top;"><ul>
+      <li><a href="graph.html#mgrid.graph.geographic.GeoGraph.inter_nodes">inter_nodes (mgrid.graph.geographic.GeoGraph attribute)</a>
 
       <ul>
-        <li><a href="grid.html#mgrid.grid.planar.PlanarGrid.inter_nodes">(mgrid.grid.planar.PlanarGrid attribute)</a>
+        <li><a href="grid.html#mgrid.grid.geographic.GeoGrid.inter_nodes">(mgrid.grid.geographic.GeoGrid attribute)</a>
 </li>
       </ul></li>
-  </ul></td>
-  <td style="width: 33%; vertical-align: top;"><ul>
       <li><a href="graph.html#mgrid.graph.supra.SupraGraph.intra_edges">intra_edges (mgrid.graph.supra.SupraGraph attribute)</a>
 </li>
-      <li><a href="graph.html#mgrid.graph.planar.PlanarGraph.intra_nodes">intra_nodes() (mgrid.graph.planar.PlanarGraph property)</a>
+      <li><a href="graph.html#mgrid.graph.geographic.GeoGraph.intra_nodes">intra_nodes() (mgrid.graph.geographic.GeoGraph property)</a>
 </li>
   </ul></td>
 </tr></table>
@@ -297,14 +336,14 @@ <h2 id="I">I</h2>
 <h2 id="L">L</h2>
 <table style="width: 100%" class="indextable genindextable"><tr>
   <td style="width: 33%; vertical-align: top;"><ul>
-      <li><a href="graph.html#mgrid.graph.planar.PlanarGraph.layer_edges">layer_edges() (mgrid.graph.planar.PlanarGraph method)</a>
+      <li><a href="graph.html#mgrid.graph.geographic.GeoGraph.layer_edges">layer_edges() (mgrid.graph.geographic.GeoGraph method)</a>
 </li>
-      <li><a href="graph.html#mgrid.graph.planar.PlanarGraph.layer_graph">layer_graph() (mgrid.graph.planar.PlanarGraph method)</a>
+      <li><a href="graph.html#mgrid.graph.geographic.GeoGraph.layer_graph">layer_graph() (mgrid.graph.geographic.GeoGraph method)</a>
 </li>
-      <li><a href="graph.html#mgrid.graph.planar.PlanarGraph.layers">layers (mgrid.graph.planar.PlanarGraph attribute)</a>
+      <li><a href="graph.html#mgrid.graph.geographic.GeoGraph.layers">layers (mgrid.graph.geographic.GeoGraph attribute)</a>
 
       <ul>
-        <li><a href="grid.html#mgrid.grid.planar.PlanarGrid.layers">(mgrid.grid.planar.PlanarGrid attribute)</a>
+        <li><a href="grid.html#mgrid.grid.geographic.GeoGrid.layers">(mgrid.grid.geographic.GeoGrid attribute)</a>
 </li>
       </ul></li>
   </ul></td>
@@ -322,10 +361,10 @@ <h2 id="M">M</h2>
       <li><a href="power_flow.html#mgrid.power_flow.delivery.Cable.max_i_ka">max_i_ka (mgrid.power_flow.delivery.Cable attribute)</a>
 </li>
       <li>
-    mgrid.graph.planar
+    mgrid.graph.geographic
 
       <ul>
-        <li><a href="graph.html#module-mgrid.graph.planar">module</a>
+        <li><a href="graph.html#module-mgrid.graph.geographic">module</a>
 </li>
       </ul></li>
       <li>
@@ -336,10 +375,10 @@ <h2 id="M">M</h2>
 </li>
       </ul></li>
       <li>
-    mgrid.grid.planar
+    mgrid.grid.geographic
 
       <ul>
-        <li><a href="grid.html#module-mgrid.grid.planar">module</a>
+        <li><a href="grid.html#module-mgrid.grid.geographic">module</a>
 </li>
       </ul></li>
       <li>
@@ -368,11 +407,25 @@ <h2 id="M">M</h2>
 
       <ul>
         <li><a href="power_flow.html#module-mgrid.power_flow.pandapower">module</a>
+</li>
+      </ul></li>
+      <li>
+    mgrid.power_flow.series
+
+      <ul>
+        <li><a href="snapshots.html#module-mgrid.power_flow.series">module</a>
 </li>
       </ul></li>
   </ul></td>
   <td style="width: 33%; vertical-align: top;"><ul>
       <li>
+    mgrid.power_flow.snapshot
+
+      <ul>
+        <li><a href="snapshots.html#module-mgrid.power_flow.snapshot">module</a>
+</li>
+      </ul></li>
+      <li>
     mgrid.power_flow.type
 
       <ul>
@@ -390,11 +443,11 @@ <h2 id="M">M</h2>
     module
 
       <ul>
-        <li><a href="graph.html#module-mgrid.graph.planar">mgrid.graph.planar</a>
+        <li><a href="graph.html#module-mgrid.graph.geographic">mgrid.graph.geographic</a>
 </li>
         <li><a href="graph.html#module-mgrid.graph.supra">mgrid.graph.supra</a>
 </li>
-        <li><a href="grid.html#module-mgrid.grid.planar">mgrid.grid.planar</a>
+        <li><a href="grid.html#module-mgrid.grid.geographic">mgrid.grid.geographic</a>
 </li>
         <li><a href="grid.html#module-mgrid.grid.supra">mgrid.grid.supra</a>
 </li>
@@ -403,6 +456,10 @@ <h2 id="M">M</h2>
         <li><a href="power_flow.html#module-mgrid.power_flow.delivery">mgrid.power_flow.delivery</a>
 </li>
         <li><a href="power_flow.html#module-mgrid.power_flow.pandapower">mgrid.power_flow.pandapower</a>
+</li>
+        <li><a href="snapshots.html#module-mgrid.power_flow.series">mgrid.power_flow.series</a>
+</li>
+        <li><a href="snapshots.html#module-mgrid.power_flow.snapshot">mgrid.power_flow.snapshot</a>
 </li>
         <li><a href="power_flow.html#module-mgrid.power_flow.type">mgrid.power_flow.type</a>
 </li>
@@ -423,12 +480,10 @@ <h2 id="N">N</h2>
       </ul></li>
   </ul></td>
   <td style="width: 33%; vertical-align: top;"><ul>
-      <li><a href="graph.html#mgrid.graph.supra.SupraGraph.nodelist">nodelist (mgrid.graph.supra.SupraGraph attribute)</a>
-
-      <ul>
-        <li><a href="grid.html#mgrid.grid.planar.PlanarGrid.nodelist">(mgrid.grid.planar.PlanarGrid attribute)</a>
+      <li><a href="grid.html#mgrid.grid.geographic.GeoGrid.nodelist">nodelist (mgrid.grid.geographic.GeoGrid attribute)</a>
+</li>
+      <li><a href="graph.html#mgrid.graph.supra.SupraGraph.nodes_new">nodes_new() (mgrid.graph.supra.SupraGraph property)</a>
 </li>
-      </ul></li>
   </ul></td>
 </tr></table>
 
@@ -450,12 +505,10 @@ <h2 id="P">P</h2>
       <li><a href="power_flow.html#mgrid.power_flow.delivery.CablePhase.phases">phases (mgrid.power_flow.delivery.CablePhase attribute)</a>
 </li>
       <li><a href="transformation.html#mgrid.transformation.planar2supra">planar2supra() (in module mgrid.transformation)</a>
-</li>
-      <li><a href="graph.html#mgrid.graph.planar.PlanarGraph">PlanarGraph (class in mgrid.graph.planar)</a>
-</li>
-      <li><a href="grid.html#mgrid.grid.planar.PlanarGrid">PlanarGrid (class in mgrid.grid.planar)</a>
 </li>
       <li><a href="power_flow.html#mgrid.power_flow.conversion.Ejection.power_factor">power_factor (mgrid.power_flow.conversion.Ejection attribute)</a>
+</li>
+      <li><a href="snapshots.html#mgrid.power_flow.snapshot.Snapshot.previous">previous (mgrid.power_flow.snapshot.Snapshot attribute)</a>
 </li>
   </ul></td>
 </tr></table>
@@ -476,10 +529,14 @@ <h2 id="R">R</h2>
 <table style="width: 100%" class="indextable genindextable"><tr>
   <td style="width: 33%; vertical-align: top;"><ul>
       <li><a href="power_flow.html#mgrid.power_flow.delivery.Cable.r_ohm">r_ohm (mgrid.power_flow.delivery.Cable attribute)</a>
+</li>
+      <li><a href="power_flow.html#mgrid.power_flow.delivery.CablePhase.r_ohm_mat">r_ohm_mat (mgrid.power_flow.delivery.CablePhase attribute)</a>
 </li>
   </ul></td>
   <td style="width: 33%; vertical-align: top;"><ul>
-      <li><a href="power_flow.html#mgrid.power_flow.delivery.CablePhase.r_ohm_mat">r_ohm_mat (mgrid.power_flow.delivery.CablePhase attribute)</a>
+      <li><a href="snapshots.html#mgrid.power_flow.snapshot.Snapshot.result_pandapower">result_pandapower() (mgrid.power_flow.snapshot.Snapshot method)</a>
+</li>
+      <li><a href="snapshots.html#mgrid.power_flow.snapshot.Snapshot.result_pypsa">result_pypsa() (mgrid.power_flow.snapshot.Snapshot method)</a>
 </li>
   </ul></td>
 </tr></table>
@@ -493,14 +550,18 @@ <h2 id="S">S</h2>
 </li>
       <li><a href="power_flow.html#mgrid.power_flow.conversion.SlackMulti">SlackMulti (class in mgrid.power_flow.conversion)</a>
 </li>
+      <li><a href="snapshots.html#mgrid.power_flow.snapshot.Snapshot">Snapshot (class in mgrid.power_flow.snapshot)</a>
+</li>
+      <li><a href="snapshots.html#mgrid.power_flow.series.SnapshotSeries">SnapshotSeries (class in mgrid.power_flow.series)</a>
+</li>
+  </ul></td>
+  <td style="width: 33%; vertical-align: top;"><ul>
       <li><a href="power_flow.html#mgrid.power_flow.delivery.CableStd.std_type">std_type (mgrid.power_flow.delivery.CableStd attribute)</a>
 
       <ul>
         <li><a href="power_flow.html#mgrid.power_flow.delivery.TransformerStd.std_type">(mgrid.power_flow.delivery.TransformerStd attribute)</a>
 </li>
       </ul></li>
-  </ul></td>
-  <td style="width: 33%; vertical-align: top;"><ul>
       <li><a href="power_flow.html#mgrid.power_flow.pandapower.supra2pandapower">supra2pandapower() (in module mgrid.power_flow.pandapower)</a>
 </li>
       <li><a href="graph.html#mgrid.graph.supra.SupraGraph">SupraGraph (class in mgrid.graph.supra)</a>
@@ -544,6 +605,10 @@ <h2 id="U">U</h2>
 </li>
       </ul></li>
   </ul></td>
+  <td style="width: 33%; vertical-align: top;"><ul>
+      <li><a href="snapshots.html#mgrid.power_flow.snapshot.Snapshot.update_previsou">update_previsou() (mgrid.power_flow.snapshot.Snapshot method)</a>
+</li>
+  </ul></td>
 </tr></table>
 
 <h2 id="V">V</h2>
@@ -553,13 +618,15 @@ <h2 id="V">V</h2>
 </li>
       <li><a href="power_flow.html#mgrid.power_flow.type.TransformerType.v_low_kv">v_low_kv (mgrid.power_flow.type.TransformerType attribute)</a>
 </li>
-  </ul></td>
-  <td style="width: 33%; vertical-align: top;"><ul>
       <li><a href="power_flow.html#mgrid.power_flow.type.TransformerType.vk_percent">vk_percent (mgrid.power_flow.type.TransformerType attribute)</a>
 </li>
+  </ul></td>
+  <td style="width: 33%; vertical-align: top;"><ul>
       <li><a href="power_flow.html#mgrid.power_flow.type.TransformerType.vkr_percent">vkr_percent (mgrid.power_flow.type.TransformerType attribute)</a>
 </li>
       <li><a href="power_flow.html#mgrid.power_flow.conversion.Slack.vm_pu">vm_pu (mgrid.power_flow.conversion.Slack attribute)</a>
+</li>
+      <li><a href="snapshots.html#mgrid.power_flow.snapshot.Snapshot.voltages">voltages (mgrid.power_flow.snapshot.Snapshot attribute)</a>
 </li>
   </ul></td>
 </tr></table>
diff --git a/docs/graph.html b/docs/graph.html
index 16100b1..561f666 100644
--- a/docs/graph.html
+++ b/docs/graph.html
@@ -90,13 +90,14 @@
 
               <ul class="current">
 <li class="toctree-l1 current"><a class="current reference internal" href="#">Graph Theoretic Model</a><ul>
-<li class="toctree-l2"><a class="reference internal" href="#module-mgrid.graph.planar">Planar Graph</a></li>
+<li class="toctree-l2"><a class="reference internal" href="#module-mgrid.graph.geographic">Geographic Graph</a></li>
 <li class="toctree-l2"><a class="reference internal" href="#module-mgrid.graph.supra">Supra Graph</a></li>
 </ul>
 </li>
 <li class="toctree-l1"><a class="reference internal" href="grid.html">Power Grid</a></li>
-<li class="toctree-l1"><a class="reference internal" href="power_flow.html">Power Flow Calculation</a></li>
 <li class="toctree-l1"><a class="reference internal" href="transformation.html">Transformation</a></li>
+<li class="toctree-l1"><a class="reference internal" href="power_flow.html">Power Flow Calculation</a></li>
+<li class="toctree-l1"><a class="reference internal" href="snapshots.html">Snapshot</a></li>
 </ul>
 <ul>
 <li class="toctree-l1"><a class="reference internal" href="bibliography.html">Bibliography</a></li>
@@ -169,26 +170,29 @@
 
   <div class="section" id="graph-theoretic-model">
 <h1>Graph Theoretic Model<a class="headerlink" href="#graph-theoretic-model" title="Permalink to this headline">¶</a></h1>
-<div class="section" id="module-mgrid.graph.planar">
-<span id="planar-graph"></span><h2>Planar Graph<a class="headerlink" href="#module-mgrid.graph.planar" title="Permalink to this headline">¶</a></h2>
-<p>A class for planar graph corresponding to a multilayer network.</p>
-<p>All the nodes and edges in a planar graph can have geographical
-attributes.</p>
+<div class="section" id="module-mgrid.graph.geographic">
+<span id="geographic-graph"></span><h2>Geographic Graph<a class="headerlink" href="#module-mgrid.graph.geographic" title="Permalink to this headline">¶</a></h2>
+<p>A class for geographic graph corresponding to a multilayer network.</p>
+<p>Geographic graph is a unique concept in this project. Due to the fact
+that there is no duplicated intra-nodes in different layers, all the
+intra-edges can be included in one simple graph (without parallel edge).
+Furthermore, inter-nodes represent transformers in power systems, so
+they are geographical points. That is, all the nodes and edges in a
+planar graph have geographical attributes.</p>
 <dl class="py class">
-<dt id="mgrid.graph.planar.PlanarGraph">
-<em class="property"><span class="pre">class</span> </em><code class="sig-prename descclassname"><span class="pre">mgrid.graph.planar.</span></code><code class="sig-name descname"><span class="pre">PlanarGraph</span></code><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">dg</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em><span class="sig-paren">)</span><a class="reference internal" href="_modules/mgrid/graph/planar.html#PlanarGraph"><span class="viewcode-link"><span class="pre">[source]</span></span></a><a class="headerlink" href="#mgrid.graph.planar.PlanarGraph" title="Permalink to this definition">¶</a></dt>
+<dt id="mgrid.graph.geographic.GeoGraph">
+<em class="property"><span class="pre">class</span> </em><code class="sig-prename descclassname"><span class="pre">mgrid.graph.geographic.</span></code><code class="sig-name descname"><span class="pre">GeoGraph</span></code><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">dg</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em><span class="sig-paren">)</span><a class="reference internal" href="_modules/mgrid/graph/geographic.html#GeoGraph"><span class="viewcode-link"><span class="pre">[source]</span></span></a><a class="headerlink" href="#mgrid.graph.geographic.GeoGraph" title="Permalink to this definition">¶</a></dt>
 <dd><p>Bases: <code class="xref py py-class docutils literal notranslate"><span class="pre">networkx.classes.digraph.DiGraph</span></code></p>
-<p>Multilayer network in form of planar graph.</p>
+<p>Multilayer network as a planar graph.</p>
 <div class="admonition note">
 <p class="admonition-title">Note</p>
-<p>There are two kinds of nodes, inter-nodes and planar nodes. If
-an inter-node is isolated in some layer, it cannot be recognised
-directly. Use method <code class="docutils literal notranslate"><span class="pre">add_inter_node</span></code> to specify those
-inter-nodes.</p>
+<p><code class="docutils literal notranslate"><span class="pre">DiGraph</span></code> from <code class="docutils literal notranslate"><span class="pre">networkx</span></code> is inherited, in order to modify
+terminals of edges directly. The order of edge terminals
+returned by <code class="docutils literal notranslate"><span class="pre">Graph</span></code> class is not consistent.</p>
 </div>
 <dl class="py attribute">
-<dt id="mgrid.graph.planar.PlanarGraph.inter_nodes">
-<code class="sig-name descname"><span class="pre">inter_nodes</span></code><a class="headerlink" href="#mgrid.graph.planar.PlanarGraph.inter_nodes" title="Permalink to this definition">¶</a></dt>
+<dt id="mgrid.graph.geographic.GeoGraph.inter_nodes">
+<code class="sig-name descname"><span class="pre">inter_nodes</span></code><a class="headerlink" href="#mgrid.graph.geographic.GeoGraph.inter_nodes" title="Permalink to this definition">¶</a></dt>
 <dd><p>information on inter-nodes.</p>
 <table class="docutils align-default">
 <colgroup>
@@ -225,8 +229,8 @@ <h1>Graph Theoretic Model<a class="headerlink" href="#graph-theoretic-model" tit
 </dd></dl>
 
 <dl class="py attribute">
-<dt id="mgrid.graph.planar.PlanarGraph.layers">
-<code class="sig-name descname"><span class="pre">layers</span></code><a class="headerlink" href="#mgrid.graph.planar.PlanarGraph.layers" title="Permalink to this definition">¶</a></dt>
+<dt id="mgrid.graph.geographic.GeoGraph.layers">
+<code class="sig-name descname"><span class="pre">layers</span></code><a class="headerlink" href="#mgrid.graph.geographic.GeoGraph.layers" title="Permalink to this definition">¶</a></dt>
 <dd><p>integer indices of all the layers.</p>
 <dl class="field-list simple">
 <dt class="field-odd">Type</dt>
@@ -236,8 +240,8 @@ <h1>Graph Theoretic Model<a class="headerlink" href="#graph-theoretic-model" tit
 </dd></dl>
 
 <dl class="py attribute">
-<dt id="mgrid.graph.planar.PlanarGraph.df_layers">
-<code class="sig-name descname"><span class="pre">df_layers</span></code><a class="headerlink" href="#mgrid.graph.planar.PlanarGraph.df_layers" title="Permalink to this definition">¶</a></dt>
+<dt id="mgrid.graph.geographic.GeoGraph.df_layers">
+<code class="sig-name descname"><span class="pre">df_layers</span></code><a class="headerlink" href="#mgrid.graph.geographic.GeoGraph.df_layers" title="Permalink to this definition">¶</a></dt>
 <dd><p>information on layers.</p>
 <table class="docutils align-default">
 <colgroup>
@@ -270,8 +274,8 @@ <h1>Graph Theoretic Model<a class="headerlink" href="#graph-theoretic-model" tit
 </dd></dl>
 
 <dl class="py method">
-<dt id="mgrid.graph.planar.PlanarGraph.__init__">
-<code class="sig-name descname"><span class="pre">__init__</span></code><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">dg</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em><span class="sig-paren">)</span><a class="reference internal" href="_modules/mgrid/graph/planar.html#PlanarGraph.__init__"><span class="viewcode-link"><span class="pre">[source]</span></span></a><a class="headerlink" href="#mgrid.graph.planar.PlanarGraph.__init__" title="Permalink to this definition">¶</a></dt>
+<dt id="mgrid.graph.geographic.GeoGraph.__init__">
+<code class="sig-name descname"><span class="pre">__init__</span></code><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">dg</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em><span class="sig-paren">)</span><a class="reference internal" href="_modules/mgrid/graph/geographic.html#GeoGraph.__init__"><span class="viewcode-link"><span class="pre">[source]</span></span></a><a class="headerlink" href="#mgrid.graph.geographic.GeoGraph.__init__" title="Permalink to this definition">¶</a></dt>
 <dd><p>Init an empty directed graph or from existing directed graph.</p>
 <dl class="field-list simple">
 <dt class="field-odd">Parameters</dt>
@@ -281,12 +285,12 @@ <h1>Graph Theoretic Model<a class="headerlink" href="#graph-theoretic-model" tit
 </dd></dl>
 
 <dl class="py method">
-<dt id="mgrid.graph.planar.PlanarGraph.add_inter_node">
-<code class="sig-name descname"><span class="pre">add_inter_node</span></code><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">name</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">upper</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">True</span></span></em><span class="sig-paren">)</span><a class="reference internal" href="_modules/mgrid/graph/planar.html#PlanarGraph.add_inter_node"><span class="viewcode-link"><span class="pre">[source]</span></span></a><a class="headerlink" href="#mgrid.graph.planar.PlanarGraph.add_inter_node" title="Permalink to this definition">¶</a></dt>
-<dd><p>Specify a planar node as an inter-node with an adjacent layer.</p>
-<p>Sometimes, one terminal of an inter-edge is an isolated node in some
-layer, then it will not be recognised as an inter-node. It must be
-specified manually.</p>
+<dt id="mgrid.graph.geographic.GeoGraph.add_inter_node">
+<code class="sig-name descname"><span class="pre">add_inter_node</span></code><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">name</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">upper</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">True</span></span></em><span class="sig-paren">)</span><a class="reference internal" href="_modules/mgrid/graph/geographic.html#GeoGraph.add_inter_node"><span class="viewcode-link"><span class="pre">[source]</span></span></a><a class="headerlink" href="#mgrid.graph.geographic.GeoGraph.add_inter_node" title="Permalink to this definition">¶</a></dt>
+<dd><p>Specify a planar node as inter-node with an adjacent layer.</p>
+<p>Sometimes, one terminal of an inter-edge is an isolated node in
+some layer, then it will not be recognised as an inter-node. It
+must be specified manually.</p>
 <div class="admonition warning">
 <p class="admonition-title">Warning</p>
 <p>Upper layer has a smaller integer index.</p>
@@ -303,8 +307,8 @@ <h1>Graph Theoretic Model<a class="headerlink" href="#graph-theoretic-model" tit
 </dd></dl>
 
 <dl class="py method">
-<dt id="mgrid.graph.planar.PlanarGraph.find_layer">
-<code class="sig-name descname"><span class="pre">find_layer</span></code><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">node</span></span></em><span class="sig-paren">)</span><a class="reference internal" href="_modules/mgrid/graph/planar.html#PlanarGraph.find_layer"><span class="viewcode-link"><span class="pre">[source]</span></span></a><a class="headerlink" href="#mgrid.graph.planar.PlanarGraph.find_layer" title="Permalink to this definition">¶</a></dt>
+<dt id="mgrid.graph.geographic.GeoGraph.find_layer">
+<code class="sig-name descname"><span class="pre">find_layer</span></code><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">node</span></span></em><span class="sig-paren">)</span><a class="reference internal" href="_modules/mgrid/graph/geographic.html#GeoGraph.find_layer"><span class="viewcode-link"><span class="pre">[source]</span></span></a><a class="headerlink" href="#mgrid.graph.geographic.GeoGraph.find_layer" title="Permalink to this definition">¶</a></dt>
 <dd><p>Find layer(s) of a given node.</p>
 <div class="admonition note">
 <p class="admonition-title">Note</p>
@@ -329,8 +333,8 @@ <h1>Graph Theoretic Model<a class="headerlink" href="#graph-theoretic-model" tit
 </dd></dl>
 
 <dl class="py method">
-<dt id="mgrid.graph.planar.PlanarGraph.from_edgelist">
-<em class="property"><span class="pre">classmethod</span> </em><code class="sig-name descname"><span class="pre">from_edgelist</span></code><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">df</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">source</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">target</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">element</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em><span class="sig-paren">)</span><a class="reference internal" href="_modules/mgrid/graph/planar.html#PlanarGraph.from_edgelist"><span class="viewcode-link"><span class="pre">[source]</span></span></a><a class="headerlink" href="#mgrid.graph.planar.PlanarGraph.from_edgelist" title="Permalink to this definition">¶</a></dt>
+<dt id="mgrid.graph.geographic.GeoGraph.from_edgelist">
+<em class="property"><span class="pre">classmethod</span> </em><code class="sig-name descname"><span class="pre">from_edgelist</span></code><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">df</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">source</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">target</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">element</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em><span class="sig-paren">)</span><a class="reference internal" href="_modules/mgrid/graph/geographic.html#GeoGraph.from_edgelist"><span class="viewcode-link"><span class="pre">[source]</span></span></a><a class="headerlink" href="#mgrid.graph.geographic.GeoGraph.from_edgelist" title="Permalink to this definition">¶</a></dt>
 <dd><p>Init a planar graph from an edgelist dataframe.</p>
 <dl class="field-list simple">
 <dt class="field-odd">Parameters</dt>
@@ -372,15 +376,15 @@ <h1>Graph Theoretic Model<a class="headerlink" href="#graph-theoretic-model" tit
 </dd></dl>
 
 <dl class="py method">
-<dt id="mgrid.graph.planar.PlanarGraph.intra_nodes">
-<em class="property"><span class="pre">property</span> </em><code class="sig-name descname"><span class="pre">intra_nodes</span></code><a class="headerlink" href="#mgrid.graph.planar.PlanarGraph.intra_nodes" title="Permalink to this definition">¶</a></dt>
+<dt id="mgrid.graph.geographic.GeoGraph.intra_nodes">
+<em class="property"><span class="pre">property</span> </em><code class="sig-name descname"><span class="pre">intra_nodes</span></code><a class="headerlink" href="#mgrid.graph.geographic.GeoGraph.intra_nodes" title="Permalink to this definition">¶</a></dt>
 <dd><p>Gather all the intra-nodes in a dataframe.</p>
 <dl class="field-list simple">
 <dt class="field-odd">Return type</dt>
 <dd class="field-odd"><p><code class="xref py py-class docutils literal notranslate"><span class="pre">DataFrame</span></code></p>
 </dd>
 <dt class="field-even">Returns</dt>
-<dd class="field-even"><p><p>A dataframe for intra-nodes.</p>
+<dd class="field-even"><p><p>Information on intra-nodes.</p>
 <table class="docutils align-default">
 <colgroup>
 <col style="width: 33%" />
@@ -410,8 +414,8 @@ <h1>Graph Theoretic Model<a class="headerlink" href="#graph-theoretic-model" tit
 </dd></dl>
 
 <dl class="py method">
-<dt id="mgrid.graph.planar.PlanarGraph.layer_edges">
-<code class="sig-name descname"><span class="pre">layer_edges</span></code><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">layer</span></span></em><span class="sig-paren">)</span><a class="reference internal" href="_modules/mgrid/graph/planar.html#PlanarGraph.layer_edges"><span class="viewcode-link"><span class="pre">[source]</span></span></a><a class="headerlink" href="#mgrid.graph.planar.PlanarGraph.layer_edges" title="Permalink to this definition">¶</a></dt>
+<dt id="mgrid.graph.geographic.GeoGraph.layer_edges">
+<code class="sig-name descname"><span class="pre">layer_edges</span></code><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">layer</span></span></em><span class="sig-paren">)</span><a class="reference internal" href="_modules/mgrid/graph/geographic.html#GeoGraph.layer_edges"><span class="viewcode-link"><span class="pre">[source]</span></span></a><a class="headerlink" href="#mgrid.graph.geographic.GeoGraph.layer_edges" title="Permalink to this definition">¶</a></dt>
 <dd><p>Gather all the edges and edge attributes in one layer.</p>
 <dl class="field-list simple">
 <dt class="field-odd">Parameters</dt>
@@ -427,8 +431,8 @@ <h1>Graph Theoretic Model<a class="headerlink" href="#graph-theoretic-model" tit
 </dd></dl>
 
 <dl class="py method">
-<dt id="mgrid.graph.planar.PlanarGraph.layer_graph">
-<code class="sig-name descname"><span class="pre">layer_graph</span></code><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">layer</span></span></em><span class="sig-paren">)</span><a class="reference internal" href="_modules/mgrid/graph/planar.html#PlanarGraph.layer_graph"><span class="viewcode-link"><span class="pre">[source]</span></span></a><a class="headerlink" href="#mgrid.graph.planar.PlanarGraph.layer_graph" title="Permalink to this definition">¶</a></dt>
+<dt id="mgrid.graph.geographic.GeoGraph.layer_graph">
+<code class="sig-name descname"><span class="pre">layer_graph</span></code><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">layer</span></span></em><span class="sig-paren">)</span><a class="reference internal" href="_modules/mgrid/graph/geographic.html#GeoGraph.layer_graph"><span class="viewcode-link"><span class="pre">[source]</span></span></a><a class="headerlink" href="#mgrid.graph.geographic.GeoGraph.layer_graph" title="Permalink to this definition">¶</a></dt>
 <dd><p>Build a directed graph for one layer.</p>
 <div class="admonition note">
 <p class="admonition-title">Note</p>
@@ -452,7 +456,7 @@ <h1>Graph Theoretic Model<a class="headerlink" href="#graph-theoretic-model" tit
 </div>
 <div class="section" id="module-mgrid.graph.supra">
 <span id="supra-graph"></span><h2>Supra Graph<a class="headerlink" href="#module-mgrid.graph.supra" title="Permalink to this headline">¶</a></h2>
-<p>Class for multilayer network in supra graph format.</p>
+<p>Class for multilayer network in supra-graph format.</p>
 <dl class="py class">
 <dt id="mgrid.graph.supra.SupraGraph">
 <em class="property"><span class="pre">class</span> </em><code class="sig-prename descclassname"><span class="pre">mgrid.graph.supra.</span></code><code class="sig-name descname"><span class="pre">SupraGraph</span></code><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">dg</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em><span class="sig-paren">)</span><a class="reference internal" href="_modules/mgrid/graph/supra.html#SupraGraph"><span class="viewcode-link"><span class="pre">[source]</span></span></a><a class="headerlink" href="#mgrid.graph.supra.SupraGraph" title="Permalink to this definition">¶</a></dt>
@@ -564,11 +568,34 @@ <h1>Graph Theoretic Model<a class="headerlink" href="#graph-theoretic-model" tit
 </dl>
 </dd></dl>
 
-<dl class="py attribute">
-<dt id="mgrid.graph.supra.SupraGraph.nodelist">
-<code class="sig-name descname"><span class="pre">nodelist</span></code><a class="headerlink" href="#mgrid.graph.supra.SupraGraph.nodelist" title="Permalink to this definition">¶</a></dt>
-<dd><p>sorted nodelist containing layer
-information.</p>
+<dl class="py method">
+<dt id="mgrid.graph.supra.SupraGraph.__init__">
+<code class="sig-name descname"><span class="pre">__init__</span></code><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">dg</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em><span class="sig-paren">)</span><a class="reference internal" href="_modules/mgrid/graph/supra.html#SupraGraph.__init__"><span class="viewcode-link"><span class="pre">[source]</span></span></a><a class="headerlink" href="#mgrid.graph.supra.SupraGraph.__init__" title="Permalink to this definition">¶</a></dt>
+<dd><p>Init an empty directed graph or existing directed graph.</p>
+<div class="admonition note">
+<p class="admonition-title">Note</p>
+<p>It is essential to have the option for empty graph, or some
+built-in <code class="docutils literal notranslate"><span class="pre">networkx</span></code> function will not work. Don’t know
+why.</p>
+</div>
+<dl class="field-list simple">
+<dt class="field-odd">Parameters</dt>
+<dd class="field-odd"><p><strong>dg</strong> (<code class="xref py py-data docutils literal notranslate"><span class="pre">Optional</span></code>[<code class="xref py py-class docutils literal notranslate"><span class="pre">DiGraph</span></code>]) – an existing directed graph. Default to be None.</p>
+</dd>
+</dl>
+</dd></dl>
+
+<dl class="py method">
+<dt id="mgrid.graph.supra.SupraGraph.nodes_new">
+<em class="property"><span class="pre">property</span> </em><code class="sig-name descname"><span class="pre">nodes_new</span></code><a class="headerlink" href="#mgrid.graph.supra.SupraGraph.nodes_new" title="Permalink to this definition">¶</a></dt>
+<dd><p>Gather information on terminals of inter-edges.</p>
+<dl class="field-list simple">
+<dt class="field-odd">Return type</dt>
+<dd class="field-odd"><p><code class="xref py py-class docutils literal notranslate"><span class="pre">DataFrame</span></code></p>
+</dd>
+<dt class="field-even">Returns</dt>
+<dd class="field-even"><p><p>Correspondance between original nodes, layers and buses for
+terminals of inter-edges.</p>
 <table class="docutils align-default">
 <colgroup>
 <col style="width: 33%" />
@@ -582,40 +609,21 @@ <h1>Graph Theoretic Model<a class="headerlink" href="#graph-theoretic-model" tit
 </tr>
 </thead>
 <tbody>
-<tr class="row-even"><td><p>node (index)</p></td>
+<tr class="row-even"><td><p>origin (index)</p></td>
 <td><p>object</p></td>
-<td><p>node name</p></td>
+<td><p>node in geographic graph</p></td>
 </tr>
-<tr class="row-odd"><td><p>idx</p></td>
+<tr class="row-odd"><td><p>layer (index)</p></td>
 <td><p>int64</p></td>
-<td><p>layer to which node belongs</p></td>
+<td><p>to which layer the node belongs</p></td>
 </tr>
-<tr class="row-even"><td><p>name</p></td>
+<tr class="row-even"><td><p>bus</p></td>
 <td><p>object</p></td>
-<td><p>layer name</p></td>
+<td><p>node name in supra graph</p></td>
 </tr>
 </tbody>
 </table>
-<dl class="field-list simple">
-<dt class="field-odd">Type</dt>
-<dd class="field-odd"><p>DataFrame</p>
-</dd>
-</dl>
-</dd></dl>
-
-<dl class="py method">
-<dt id="mgrid.graph.supra.SupraGraph.__init__">
-<code class="sig-name descname"><span class="pre">__init__</span></code><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">dg</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em><span class="sig-paren">)</span><a class="reference internal" href="_modules/mgrid/graph/supra.html#SupraGraph.__init__"><span class="viewcode-link"><span class="pre">[source]</span></span></a><a class="headerlink" href="#mgrid.graph.supra.SupraGraph.__init__" title="Permalink to this definition">¶</a></dt>
-<dd><p>Init an empty directed graph or existing directed graph.</p>
-<div class="admonition note">
-<p class="admonition-title">Note</p>
-<p>It is essential to have the option for empty graph, or some
-built-in <code class="docutils literal notranslate"><span class="pre">networkx</span></code> function will not work. Don’t know
-why.</p>
-</div>
-<dl class="field-list simple">
-<dt class="field-odd">Parameters</dt>
-<dd class="field-odd"><p><strong>dg</strong> (<code class="xref py py-data docutils literal notranslate"><span class="pre">Optional</span></code>[<code class="xref py py-class docutils literal notranslate"><span class="pre">DiGraph</span></code>]) – an existing directed graph. Default to be None.</p>
+</p>
 </dd>
 </dl>
 </dd></dl>
diff --git a/docs/grid.html b/docs/grid.html
index a4f81c7..69c4377 100644
--- a/docs/grid.html
+++ b/docs/grid.html
@@ -38,7 +38,7 @@
 
     <link rel="index" title="Index" href="genindex.html" />
     <link rel="search" title="Search" href="search.html" />
-    <link rel="next" title="Power Flow Calculation" href="power_flow.html" />
+    <link rel="next" title="Transformation" href="transformation.html" />
     <link rel="prev" title="Graph Theoretic Model" href="graph.html" />
 </head>
 
@@ -91,12 +91,13 @@
               <ul class="current">
 <li class="toctree-l1"><a class="reference internal" href="graph.html">Graph Theoretic Model</a></li>
 <li class="toctree-l1 current"><a class="current reference internal" href="#">Power Grid</a><ul>
-<li class="toctree-l2"><a class="reference internal" href="#module-mgrid.grid.planar">as Planar Graph</a></li>
+<li class="toctree-l2"><a class="reference internal" href="#module-mgrid.grid.geographic">as Geographic Graph</a></li>
 <li class="toctree-l2"><a class="reference internal" href="#module-mgrid.grid.supra">as Supra Graph</a></li>
 </ul>
 </li>
-<li class="toctree-l1"><a class="reference internal" href="power_flow.html">Power Flow Calculation</a></li>
 <li class="toctree-l1"><a class="reference internal" href="transformation.html">Transformation</a></li>
+<li class="toctree-l1"><a class="reference internal" href="power_flow.html">Power Flow Calculation</a></li>
+<li class="toctree-l1"><a class="reference internal" href="snapshots.html">Snapshot</a></li>
 </ul>
 <ul>
 <li class="toctree-l1"><a class="reference internal" href="bibliography.html">Bibliography</a></li>
@@ -169,22 +170,26 @@
 
   <div class="section" id="power-grid">
 <h1>Power Grid<a class="headerlink" href="#power-grid" title="Permalink to this headline">¶</a></h1>
-<div class="section" id="module-mgrid.grid.planar">
-<span id="as-planar-graph"></span><h2>as Planar Graph<a class="headerlink" href="#module-mgrid.grid.planar" title="Permalink to this headline">¶</a></h2>
+<div class="section" id="module-mgrid.grid.geographic">
+<span id="as-geographic-graph"></span><h2>as Geographic Graph<a class="headerlink" href="#module-mgrid.grid.geographic" title="Permalink to this headline">¶</a></h2>
 <p>Class for grid in planar graph format.</p>
 <dl class="py class">
-<dt id="mgrid.grid.planar.PlanarGrid">
-<em class="property"><span class="pre">class</span> </em><code class="sig-prename descclassname"><span class="pre">mgrid.grid.planar.</span></code><code class="sig-name descname"><span class="pre">PlanarGrid</span></code><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">dg</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em><span class="sig-paren">)</span><a class="reference internal" href="_modules/mgrid/grid/planar.html#PlanarGrid"><span class="viewcode-link"><span class="pre">[source]</span></span></a><a class="headerlink" href="#mgrid.grid.planar.PlanarGrid" title="Permalink to this definition">¶</a></dt>
-<dd><p>Bases: <a class="reference internal" href="graph.html#mgrid.graph.planar.PlanarGraph" title="mgrid.graph.planar.PlanarGraph"><code class="xref py py-class docutils literal notranslate"><span class="pre">mgrid.graph.planar.PlanarGraph</span></code></a></p>
+<dt id="mgrid.grid.geographic.GeoGrid">
+<em class="property"><span class="pre">class</span> </em><code class="sig-prename descclassname"><span class="pre">mgrid.grid.geographic.</span></code><code class="sig-name descname"><span class="pre">GeoGrid</span></code><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">dg</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em><span class="sig-paren">)</span><a class="reference internal" href="_modules/mgrid/grid/geographic.html#GeoGrid"><span class="viewcode-link"><span class="pre">[source]</span></span></a><a class="headerlink" href="#mgrid.grid.geographic.GeoGrid" title="Permalink to this definition">¶</a></dt>
+<dd><p>Bases: <a class="reference internal" href="graph.html#mgrid.graph.geographic.GeoGraph" title="mgrid.graph.geographic.GeoGraph"><code class="xref py py-class docutils literal notranslate"><span class="pre">mgrid.graph.geographic.GeoGraph</span></code></a></p>
 <p>Model multilayer graph in plane by contracting inter-edges.</p>
 <div class="admonition note">
 <p class="admonition-title">Note</p>
-<p>Voltage levels of layers must be specified by updating
-<code class="docutils literal notranslate"><span class="pre">df_layers</span></code> manually.</p>
+<ul class="simple">
+<li><p>There are two kinds of nodes, inter-nodes and planar nodes. If
+an inter-node is isolated in some layer, it cannot be
+recognised directly.</p></li>
+<li><p>It is assumed that every conversion element has a unique name.</p></li>
+</ul>
 </div>
 <dl class="py attribute">
-<dt id="mgrid.grid.planar.PlanarGrid.inter_nodes">
-<code class="sig-name descname"><span class="pre">inter_nodes</span></code><a class="headerlink" href="#mgrid.grid.planar.PlanarGrid.inter_nodes" title="Permalink to this definition">¶</a></dt>
+<dt id="mgrid.grid.geographic.GeoGrid.inter_nodes">
+<code class="sig-name descname"><span class="pre">inter_nodes</span></code><a class="headerlink" href="#mgrid.grid.geographic.GeoGrid.inter_nodes" title="Permalink to this definition">¶</a></dt>
 <dd><p>information on inter-nodes.</p>
 <table class="docutils align-default">
 <colgroup>
@@ -225,8 +230,8 @@ <h1>Power Grid<a class="headerlink" href="#power-grid" title="Permalink to this
 </dd></dl>
 
 <dl class="py attribute">
-<dt id="mgrid.grid.planar.PlanarGrid.layers">
-<code class="sig-name descname"><span class="pre">layers</span></code><a class="headerlink" href="#mgrid.grid.planar.PlanarGrid.layers" title="Permalink to this definition">¶</a></dt>
+<dt id="mgrid.grid.geographic.GeoGrid.layers">
+<code class="sig-name descname"><span class="pre">layers</span></code><a class="headerlink" href="#mgrid.grid.geographic.GeoGrid.layers" title="Permalink to this definition">¶</a></dt>
 <dd><p>integer indices of all the layers.</p>
 <dl class="field-list simple">
 <dt class="field-odd">Type</dt>
@@ -236,8 +241,8 @@ <h1>Power Grid<a class="headerlink" href="#power-grid" title="Permalink to this
 </dd></dl>
 
 <dl class="py attribute">
-<dt id="mgrid.grid.planar.PlanarGrid.conversion">
-<code class="sig-name descname"><span class="pre">conversion</span></code><a class="headerlink" href="#mgrid.grid.planar.PlanarGrid.conversion" title="Permalink to this definition">¶</a></dt>
+<dt id="mgrid.grid.geographic.GeoGrid.conversions">
+<code class="sig-name descname"><span class="pre">conversions</span></code><a class="headerlink" href="#mgrid.grid.geographic.GeoGrid.conversions" title="Permalink to this definition">¶</a></dt>
 <dd><p>information on conversion elements.</p>
 <table class="docutils align-default">
 <colgroup>
@@ -278,8 +283,8 @@ <h1>Power Grid<a class="headerlink" href="#power-grid" title="Permalink to this
 </dd></dl>
 
 <dl class="py attribute">
-<dt id="mgrid.grid.planar.PlanarGrid.df_layers">
-<code class="sig-name descname"><span class="pre">df_layers</span></code><a class="headerlink" href="#mgrid.grid.planar.PlanarGrid.df_layers" title="Permalink to this definition">¶</a></dt>
+<dt id="mgrid.grid.geographic.GeoGrid.df_layers">
+<code class="sig-name descname"><span class="pre">df_layers</span></code><a class="headerlink" href="#mgrid.grid.geographic.GeoGrid.df_layers" title="Permalink to this definition">¶</a></dt>
 <dd><p>information on layers.</p>
 <table class="docutils align-default">
 <colgroup>
@@ -316,8 +321,8 @@ <h1>Power Grid<a class="headerlink" href="#power-grid" title="Permalink to this
 </dd></dl>
 
 <dl class="py attribute">
-<dt id="mgrid.grid.planar.PlanarGrid.nodelist">
-<code class="sig-name descname"><span class="pre">nodelist</span></code><a class="headerlink" href="#mgrid.grid.planar.PlanarGrid.nodelist" title="Permalink to this definition">¶</a></dt>
+<dt id="mgrid.grid.geographic.GeoGrid.nodelist">
+<code class="sig-name descname"><span class="pre">nodelist</span></code><a class="headerlink" href="#mgrid.grid.geographic.GeoGrid.nodelist" title="Permalink to this definition">¶</a></dt>
 <dd><p>sorted nodelist containing layer
 information.</p>
 <table class="docutils align-default">
@@ -359,8 +364,8 @@ <h1>Power Grid<a class="headerlink" href="#power-grid" title="Permalink to this
 </dd></dl>
 
 <dl class="py method">
-<dt id="mgrid.grid.planar.PlanarGrid.__init__">
-<code class="sig-name descname"><span class="pre">__init__</span></code><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">dg</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em><span class="sig-paren">)</span><a class="reference internal" href="_modules/mgrid/grid/planar.html#PlanarGrid.__init__"><span class="viewcode-link"><span class="pre">[source]</span></span></a><a class="headerlink" href="#mgrid.grid.planar.PlanarGrid.__init__" title="Permalink to this definition">¶</a></dt>
+<dt id="mgrid.grid.geographic.GeoGrid.__init__">
+<code class="sig-name descname"><span class="pre">__init__</span></code><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">dg</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em><span class="sig-paren">)</span><a class="reference internal" href="_modules/mgrid/grid/geographic.html#GeoGrid.__init__"><span class="viewcode-link"><span class="pre">[source]</span></span></a><a class="headerlink" href="#mgrid.grid.geographic.GeoGrid.__init__" title="Permalink to this definition">¶</a></dt>
 <dd><p>Init an empty directed graph or from existing directed graph.</p>
 <div class="admonition note">
 <p class="admonition-title">Note</p>
@@ -383,8 +388,8 @@ <h1>Power Grid<a class="headerlink" href="#power-grid" title="Permalink to this
 </dd></dl>
 
 <dl class="py method">
-<dt id="mgrid.grid.planar.PlanarGrid.add_conversion">
-<code class="sig-name descname"><span class="pre">add_conversion</span></code><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">name</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">node</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">element</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">layer</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em><span class="sig-paren">)</span><a class="reference internal" href="_modules/mgrid/grid/planar.html#PlanarGrid.add_conversion"><span class="viewcode-link"><span class="pre">[source]</span></span></a><a class="headerlink" href="#mgrid.grid.planar.PlanarGrid.add_conversion" title="Permalink to this definition">¶</a></dt>
+<dt id="mgrid.grid.geographic.GeoGrid.add_conversion">
+<code class="sig-name descname"><span class="pre">add_conversion</span></code><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">name</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">node</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">element</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">layer</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em><span class="sig-paren">)</span><a class="reference internal" href="_modules/mgrid/grid/geographic.html#GeoGrid.add_conversion"><span class="viewcode-link"><span class="pre">[source]</span></span></a><a class="headerlink" href="#mgrid.grid.geographic.GeoGrid.add_conversion" title="Permalink to this definition">¶</a></dt>
 <dd><p>Add a conversion element to the grid.</p>
 <div class="admonition note">
 <p class="admonition-title">Note</p>
@@ -397,7 +402,7 @@ <h1>Power Grid<a class="headerlink" href="#power-grid" title="Permalink to this
 <dd class="field-odd"><ul class="simple">
 <li><p><strong>name</strong> (<code class="xref py py-class docutils literal notranslate"><span class="pre">str</span></code>) – name of the conversion element.</p></li>
 <li><p><strong>node</strong> (<code class="xref py py-class docutils literal notranslate"><span class="pre">str</span></code>) – name of the node to which the element is attached.</p></li>
-<li><p><strong>element</strong> (<code class="xref py py-data docutils literal notranslate"><span class="pre">Union</span></code>[<a class="reference internal" href="power_flow.html#mgrid.power_flow.conversion.Ejection" title="mgrid.power_flow.conversion.Ejection"><code class="xref py py-class docutils literal notranslate"><span class="pre">Ejection</span></code></a>, <a class="reference internal" href="power_flow.html#mgrid.power_flow.conversion.Slack" title="mgrid.power_flow.conversion.Slack"><code class="xref py py-class docutils literal notranslate"><span class="pre">Slack</span></code></a>]) – model for the element.</p></li>
+<li><p><strong>element</strong> (<a class="reference internal" href="power_flow.html#mgrid.power_flow.conversion.Ejection" title="mgrid.power_flow.conversion.Ejection"><code class="xref py py-class docutils literal notranslate"><span class="pre">Ejection</span></code></a>) – model for the element.</p></li>
 <li><p><strong>layer</strong> (<code class="xref py py-data docutils literal notranslate"><span class="pre">Optional</span></code>[<code class="xref py py-class docutils literal notranslate"><span class="pre">str</span></code>]) – layer to which the element belongs. If <code class="docutils literal notranslate"><span class="pre">node</span></code> is an
 intra-node, it is not necessary to specify it. When
 <code class="docutils literal notranslate"><span class="pre">node</span></code> is an inter-node and it is not specified, a
@@ -408,8 +413,8 @@ <h1>Power Grid<a class="headerlink" href="#power-grid" title="Permalink to this
 </dd></dl>
 
 <dl class="py method">
-<dt id="mgrid.grid.planar.PlanarGrid.add_inter_node">
-<code class="sig-name descname"><span class="pre">add_inter_node</span></code><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">name</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">element</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">upper</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">True</span></span></em><span class="sig-paren">)</span><a class="reference internal" href="_modules/mgrid/grid/planar.html#PlanarGrid.add_inter_node"><span class="viewcode-link"><span class="pre">[source]</span></span></a><a class="headerlink" href="#mgrid.grid.planar.PlanarGrid.add_inter_node" title="Permalink to this definition">¶</a></dt>
+<dt id="mgrid.grid.geographic.GeoGrid.add_inter_node">
+<code class="sig-name descname"><span class="pre">add_inter_node</span></code><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">name</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">element</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">upper</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">True</span></span></em><span class="sig-paren">)</span><a class="reference internal" href="_modules/mgrid/grid/geographic.html#GeoGrid.add_inter_node"><span class="viewcode-link"><span class="pre">[source]</span></span></a><a class="headerlink" href="#mgrid.grid.geographic.GeoGrid.add_inter_node" title="Permalink to this definition">¶</a></dt>
 <dd><p>Specify a planar node as an inter-node with an adjacent layer.</p>
 <p>Sometimes, one terminal of an inter-edge is an isolated node in some
 layer, then it will not be recognised as an inter-node. It must be
@@ -472,15 +477,15 @@ <h1>Power Grid<a class="headerlink" href="#power-grid" title="Permalink to this
 <tbody>
 <tr class="row-even"><td><p>name (index)</p></td>
 <td><p>object</p></td>
-<td><p>name of conversion elements.</p></td>
+<td><p>name of the element.</p></td>
 </tr>
 <tr class="row-odd"><td><p>bus</p></td>
 <td><p>object</p></td>
-<td><p>buses to which elements are attached.</p></td>
+<td><p>buses to which the element is attached</p></td>
 </tr>
 <tr class="row-even"><td><p>element</p></td>
 <td><p>object</p></td>
-<td><p>element models.</p></td>
+<td><p>model</p></td>
 </tr>
 </tbody>
 </table>
@@ -502,6 +507,48 @@ <h1>Power Grid<a class="headerlink" href="#power-grid" title="Permalink to this
 </dl>
 </dd></dl>
 
+<dl class="py attribute">
+<dt id="mgrid.grid.supra.SupraGrid.buses">
+<code class="sig-name descname"><span class="pre">buses</span></code><a class="headerlink" href="#mgrid.grid.supra.SupraGrid.buses" title="Permalink to this definition">¶</a></dt>
+<dd><p>sorted list of buses.</p>
+<table class="docutils align-default">
+<colgroup>
+<col style="width: 33%" />
+<col style="width: 33%" />
+<col style="width: 33%" />
+</colgroup>
+<thead>
+<tr class="row-odd"><th class="head"><p>name</p></th>
+<th class="head"><p>dtype</p></th>
+<th class="head"><p>definition</p></th>
+</tr>
+</thead>
+<tbody>
+<tr class="row-even"><td><p>node (index)</p></td>
+<td><p>object</p></td>
+<td><p>node name</p></td>
+</tr>
+<tr class="row-odd"><td><p>idx</p></td>
+<td><p>int64</p></td>
+<td><p>layer to which node belongs</p></td>
+</tr>
+<tr class="row-even"><td><p>layer_name</p></td>
+<td><p>object</p></td>
+<td><p>name of the layer</p></td>
+</tr>
+<tr class="row-odd"><td><p>original</p></td>
+<td><p>object</p></td>
+<td><p>original node name</p></td>
+</tr>
+</tbody>
+</table>
+<dl class="field-list simple">
+<dt class="field-odd">Type</dt>
+<dd class="field-odd"><p>DataFrame</p>
+</dd>
+</dl>
+</dd></dl>
+
 <dl class="py method">
 <dt id="mgrid.grid.supra.SupraGrid.__init__">
 <code class="sig-name descname"><span class="pre">__init__</span></code><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">dg</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em><span class="sig-paren">)</span><a class="reference internal" href="_modules/mgrid/grid/supra.html#SupraGrid.__init__"><span class="viewcode-link"><span class="pre">[source]</span></span></a><a class="headerlink" href="#mgrid.grid.supra.SupraGrid.__init__" title="Permalink to this definition">¶</a></dt>
@@ -530,7 +577,7 @@ <h1>Power Grid<a class="headerlink" href="#power-grid" title="Permalink to this
           </div>
           <footer>
     <div class="rst-footer-buttons" role="navigation" aria-label="footer navigation">
-        <a href="power_flow.html" class="btn btn-neutral float-right" title="Power Flow Calculation" accesskey="n" rel="next">Next <span class="fa fa-arrow-circle-right" aria-hidden="true"></span></a>
+        <a href="transformation.html" class="btn btn-neutral float-right" title="Transformation" accesskey="n" rel="next">Next <span class="fa fa-arrow-circle-right" aria-hidden="true"></span></a>
         <a href="graph.html" class="btn btn-neutral float-left" title="Graph Theoretic Model" accesskey="p" rel="prev"><span class="fa fa-arrow-circle-left" aria-hidden="true"></span> Previous</a>
     </div>
 
diff --git a/docs/index.html b/docs/index.html
index 8e9167b..4827268 100644
--- a/docs/index.html
+++ b/docs/index.html
@@ -90,8 +90,9 @@
               <ul>
 <li class="toctree-l1"><a class="reference internal" href="graph.html">Graph Theoretic Model</a></li>
 <li class="toctree-l1"><a class="reference internal" href="grid.html">Power Grid</a></li>
-<li class="toctree-l1"><a class="reference internal" href="power_flow.html">Power Flow Calculation</a></li>
 <li class="toctree-l1"><a class="reference internal" href="transformation.html">Transformation</a></li>
+<li class="toctree-l1"><a class="reference internal" href="power_flow.html">Power Flow Calculation</a></li>
+<li class="toctree-l1"><a class="reference internal" href="snapshots.html">Snapshot</a></li>
 </ul>
 <ul>
 <li class="toctree-l1"><a class="reference internal" href="bibliography.html">Bibliography</a></li>
@@ -257,7 +258,7 @@ <h2>Three Representation Methods<a class="headerlink" href="#three-representatio
 </tr>
 </thead>
 <tbody>
-<tr class="row-even"><td><p><a class="reference internal" href="graph.html#mgrid.graph.planar.PlanarGraph" title="mgrid.graph.planar.PlanarGraph"><code class="xref py py-class docutils literal notranslate"><span class="pre">mgrid.graph.planar.PlanarGraph</span></code></a></p></td>
+<tr class="row-even"><td><p><code class="xref py py-class docutils literal notranslate"><span class="pre">mgrid.graph.planar.PlanarGraph</span></code></p></td>
 <td><p>in planar graph</p></td>
 <td><p>contracted</p></td>
 </tr>
@@ -279,15 +280,16 @@ <h2>API<a class="headerlink" href="#api" title="Permalink to this headline">¶</
 <div class="toctree-wrapper compound">
 <ul>
 <li class="toctree-l1"><a class="reference internal" href="graph.html">Graph Theoretic Model</a><ul>
-<li class="toctree-l2"><a class="reference internal" href="graph.html#module-mgrid.graph.planar">Planar Graph</a></li>
+<li class="toctree-l2"><a class="reference internal" href="graph.html#module-mgrid.graph.geographic">Geographic Graph</a></li>
 <li class="toctree-l2"><a class="reference internal" href="graph.html#module-mgrid.graph.supra">Supra Graph</a></li>
 </ul>
 </li>
 <li class="toctree-l1"><a class="reference internal" href="grid.html">Power Grid</a><ul>
-<li class="toctree-l2"><a class="reference internal" href="grid.html#module-mgrid.grid.planar">as Planar Graph</a></li>
+<li class="toctree-l2"><a class="reference internal" href="grid.html#module-mgrid.grid.geographic">as Geographic Graph</a></li>
 <li class="toctree-l2"><a class="reference internal" href="grid.html#module-mgrid.grid.supra">as Supra Graph</a></li>
 </ul>
 </li>
+<li class="toctree-l1"><a class="reference internal" href="transformation.html">Transformation</a></li>
 <li class="toctree-l1"><a class="reference internal" href="power_flow.html">Power Flow Calculation</a><ul>
 <li class="toctree-l2"><a class="reference internal" href="power_flow.html#module-mgrid.power_flow.delivery">Delivery Element</a></li>
 <li class="toctree-l2"><a class="reference internal" href="power_flow.html#module-mgrid.power_flow.conversion">Conversion Element</a></li>
@@ -295,7 +297,10 @@ <h2>API<a class="headerlink" href="#api" title="Permalink to this headline">¶</
 <li class="toctree-l2"><a class="reference internal" href="power_flow.html#module-mgrid.power_flow.pandapower">“pandapower” Package</a></li>
 </ul>
 </li>
-<li class="toctree-l1"><a class="reference internal" href="transformation.html">Transformation</a></li>
+<li class="toctree-l1"><a class="reference internal" href="snapshots.html">Snapshot</a><ul>
+<li class="toctree-l2"><a class="reference internal" href="snapshots.html#module-mgrid.power_flow.series">Snapshot Series</a></li>
+</ul>
+</li>
 </ul>
 </div>
 </div>
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diff --git a/docs/power_flow.html b/docs/power_flow.html
index 9ebfc40..ad533d2 100644
--- a/docs/power_flow.html
+++ b/docs/power_flow.html
@@ -38,8 +38,8 @@
 
     <link rel="index" title="Index" href="genindex.html" />
     <link rel="search" title="Search" href="search.html" />
-    <link rel="next" title="Transformation" href="transformation.html" />
-    <link rel="prev" title="Power Grid" href="grid.html" />
+    <link rel="next" title="Snapshot" href="snapshots.html" />
+    <link rel="prev" title="Transformation" href="transformation.html" />
 </head>
 
 <body class="wy-body-for-nav">
@@ -91,6 +91,7 @@
               <ul class="current">
 <li class="toctree-l1"><a class="reference internal" href="graph.html">Graph Theoretic Model</a></li>
 <li class="toctree-l1"><a class="reference internal" href="grid.html">Power Grid</a></li>
+<li class="toctree-l1"><a class="reference internal" href="transformation.html">Transformation</a></li>
 <li class="toctree-l1 current"><a class="current reference internal" href="#">Power Flow Calculation</a><ul>
 <li class="toctree-l2"><a class="reference internal" href="#module-mgrid.power_flow.delivery">Delivery Element</a></li>
 <li class="toctree-l2"><a class="reference internal" href="#module-mgrid.power_flow.conversion">Conversion Element</a></li>
@@ -98,7 +99,7 @@
 <li class="toctree-l2"><a class="reference internal" href="#module-mgrid.power_flow.pandapower">“pandapower” Package</a></li>
 </ul>
 </li>
-<li class="toctree-l1"><a class="reference internal" href="transformation.html">Transformation</a></li>
+<li class="toctree-l1"><a class="reference internal" href="snapshots.html">Snapshot</a></li>
 </ul>
 <ul>
 <li class="toctree-l1"><a class="reference internal" href="bibliography.html">Bibliography</a></li>
@@ -376,7 +377,7 @@ <h1>Power Flow Calculation<a class="headerlink" href="#power-flow-calculation" t
 attaches must be specified in supra graph. Furthermore, in planar graph,
 the layer of the element must be specified, because it might be attached
 to an inter-node, which spans two layers. See
-<a class="reference internal" href="grid.html#module-mgrid.grid.planar" title="mgrid.grid.planar"><code class="xref py py-mod docutils literal notranslate"><span class="pre">mgrid.grid.planar</span></code></a> for more details.</p>
+<code class="xref py py-mod docutils literal notranslate"><span class="pre">mgrid.grid.planar</span></code> for more details.</p>
 <dl class="py class">
 <dt id="mgrid.power_flow.conversion.Capacitor">
 <em class="property"><span class="pre">class</span> </em><code class="sig-prename descclassname"><span class="pre">mgrid.power_flow.conversion.</span></code><code class="sig-name descname"><span class="pre">Capacitor</span></code><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">q_mvar</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">loss_factor</span></span></em><span class="sig-paren">)</span><a class="reference internal" href="_modules/mgrid/power_flow/conversion.html#Capacitor"><span class="viewcode-link"><span class="pre">[source]</span></span></a><a class="headerlink" href="#mgrid.power_flow.conversion.Capacitor" title="Permalink to this definition">¶</a></dt>
@@ -623,8 +624,8 @@ <h1>Power Flow Calculation<a class="headerlink" href="#power-flow-calculation" t
           </div>
           <footer>
     <div class="rst-footer-buttons" role="navigation" aria-label="footer navigation">
-        <a href="transformation.html" class="btn btn-neutral float-right" title="Transformation" accesskey="n" rel="next">Next <span class="fa fa-arrow-circle-right" aria-hidden="true"></span></a>
-        <a href="grid.html" class="btn btn-neutral float-left" title="Power Grid" accesskey="p" rel="prev"><span class="fa fa-arrow-circle-left" aria-hidden="true"></span> Previous</a>
+        <a href="snapshots.html" class="btn btn-neutral float-right" title="Snapshot" accesskey="n" rel="next">Next <span class="fa fa-arrow-circle-right" aria-hidden="true"></span></a>
+        <a href="transformation.html" class="btn btn-neutral float-left" title="Transformation" accesskey="p" rel="prev"><span class="fa fa-arrow-circle-left" aria-hidden="true"></span> Previous</a>
     </div>
 
   <hr/>
diff --git a/docs/py-modindex.html b/docs/py-modindex.html
index eee4082..f52ff70 100644
--- a/docs/py-modindex.html
+++ b/docs/py-modindex.html
@@ -92,8 +92,9 @@
               <ul>
 <li class="toctree-l1"><a class="reference internal" href="graph.html">Graph Theoretic Model</a></li>
 <li class="toctree-l1"><a class="reference internal" href="grid.html">Power Grid</a></li>
-<li class="toctree-l1"><a class="reference internal" href="power_flow.html">Power Flow Calculation</a></li>
 <li class="toctree-l1"><a class="reference internal" href="transformation.html">Transformation</a></li>
+<li class="toctree-l1"><a class="reference internal" href="power_flow.html">Power Flow Calculation</a></li>
+<li class="toctree-l1"><a class="reference internal" href="snapshots.html">Snapshot</a></li>
 </ul>
 <ul>
 <li class="toctree-l1"><a class="reference internal" href="bibliography.html">Bibliography</a></li>
@@ -180,7 +181,7 @@ <h1>Python Module Index</h1>
      <tr class="cg-1">
        <td></td>
        <td>&#160;&#160;&#160;
-       <a href="graph.html#module-mgrid.graph.planar"><code class="xref">mgrid.graph.planar</code></a></td><td>
+       <a href="graph.html#module-mgrid.graph.geographic"><code class="xref">mgrid.graph.geographic</code></a></td><td>
        <em></em></td></tr>
      <tr class="cg-1">
        <td></td>
@@ -190,7 +191,7 @@ <h1>Python Module Index</h1>
      <tr class="cg-1">
        <td></td>
        <td>&#160;&#160;&#160;
-       <a href="grid.html#module-mgrid.grid.planar"><code class="xref">mgrid.grid.planar</code></a></td><td>
+       <a href="grid.html#module-mgrid.grid.geographic"><code class="xref">mgrid.grid.geographic</code></a></td><td>
        <em></em></td></tr>
      <tr class="cg-1">
        <td></td>
@@ -212,6 +213,16 @@ <h1>Python Module Index</h1>
        <td>&#160;&#160;&#160;
        <a href="power_flow.html#module-mgrid.power_flow.pandapower"><code class="xref">mgrid.power_flow.pandapower</code></a></td><td>
        <em></em></td></tr>
+     <tr class="cg-1">
+       <td></td>
+       <td>&#160;&#160;&#160;
+       <a href="snapshots.html#module-mgrid.power_flow.series"><code class="xref">mgrid.power_flow.series</code></a></td><td>
+       <em></em></td></tr>
+     <tr class="cg-1">
+       <td></td>
+       <td>&#160;&#160;&#160;
+       <a href="snapshots.html#module-mgrid.power_flow.snapshot"><code class="xref">mgrid.power_flow.snapshot</code></a></td><td>
+       <em></em></td></tr>
      <tr class="cg-1">
        <td></td>
        <td>&#160;&#160;&#160;
diff --git a/docs/search.html b/docs/search.html
index 513fcdb..23d41ee 100644
--- a/docs/search.html
+++ b/docs/search.html
@@ -92,8 +92,9 @@
               <ul>
 <li class="toctree-l1"><a class="reference internal" href="graph.html">Graph Theoretic Model</a></li>
 <li class="toctree-l1"><a class="reference internal" href="grid.html">Power Grid</a></li>
-<li class="toctree-l1"><a class="reference internal" href="power_flow.html">Power Flow Calculation</a></li>
 <li class="toctree-l1"><a class="reference internal" href="transformation.html">Transformation</a></li>
+<li class="toctree-l1"><a class="reference internal" href="power_flow.html">Power Flow Calculation</a></li>
+<li class="toctree-l1"><a class="reference internal" href="snapshots.html">Snapshot</a></li>
 </ul>
 <ul>
 <li class="toctree-l1"><a class="reference internal" href="bibliography.html">Bibliography</a></li>
diff --git a/docs/searchindex.js b/docs/searchindex.js
index abb9e63..b6dc065 100644
--- a/docs/searchindex.js
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+<li class="toctree-l1 current"><a class="current reference internal" href="#">Snapshot</a><ul>
+<li class="toctree-l2"><a class="reference internal" href="#module-mgrid.power_flow.series">Snapshot Series</a></li>
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+  <div class="section" id="module-mgrid.power_flow.snapshot">
+<span id="snapshot"></span><h1>Snapshot<a class="headerlink" href="#module-mgrid.power_flow.snapshot" title="Permalink to this headline">¶</a></h1>
+<p>Store input and calculation results in snapshots.</p>
+<p>Though the power system operates continuously, it is considered in
+discrete time in power flow calculation. That is, between two
+consecutive time indices, the system state is assumed to remain steady,
+so small variations are ignored. Usually, the duration between indices
+is long compared to the frequency of alternating current (50 Hz in
+Europe and 60 Hz in the US).</p>
+<p>The result for voltages in the previous snapshot can be used as the
+initial guess in power flow calculation.</p>
+<dl class="py class">
+<dt id="mgrid.power_flow.snapshot.Snapshot">
+<em class="property"><span class="pre">class</span> </em><code class="sig-prename descclassname"><span class="pre">mgrid.power_flow.snapshot.</span></code><code class="sig-name descname"><span class="pre">Snapshot</span></code><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">increments</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">previous</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">voltages</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">flows</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em><span class="sig-paren">)</span><a class="reference internal" href="_modules/mgrid/power_flow/snapshot.html#Snapshot"><span class="viewcode-link"><span class="pre">[source]</span></span></a><a class="headerlink" href="#mgrid.power_flow.snapshot.Snapshot" title="Permalink to this definition">¶</a></dt>
+<dd><p>Bases: <code class="xref py py-class docutils literal notranslate"><span class="pre">object</span></code></p>
+<p>Store input in incremental format and results in dataframes.</p>
+<dl class="py method">
+<dt id="mgrid.power_flow.snapshot.Snapshot.base">
+<em class="property"><span class="pre">property</span> </em><code class="sig-name descname"><span class="pre">base</span></code><a class="headerlink" href="#mgrid.power_flow.snapshot.Snapshot.base" title="Permalink to this definition">¶</a></dt>
+<dd><p>Get the base grid model and snapshot.</p>
+<dl class="field-list simple">
+<dt class="field-odd">Returns</dt>
+<dd class="field-odd"><p>[description]</p>
+</dd>
+<dt class="field-even">Return type</dt>
+<dd class="field-even"><p>[type]</p>
+</dd>
+</dl>
+</dd></dl>
+
+<dl class="py attribute">
+<dt id="mgrid.power_flow.snapshot.Snapshot.flows">
+<code class="sig-name descname"><span class="pre">flows</span></code><em class="property"><span class="pre">:</span> <span class="pre">Optional</span><span class="p"><span class="pre">[</span></span><span class="pre">pandas.core.frame.DataFrame</span><span class="p"><span class="pre">]</span></span></em><em class="property"> <span class="pre">=</span> <span class="pre">None</span></em><a class="headerlink" href="#mgrid.power_flow.snapshot.Snapshot.flows" title="Permalink to this definition">¶</a></dt>
+<dd><p>power flow along edges in kW</p>
+</dd></dl>
+
+<dl class="py attribute">
+<dt id="mgrid.power_flow.snapshot.Snapshot.increments">
+<code class="sig-name descname"><span class="pre">increments</span></code><em class="property"><span class="pre">:</span> <span class="pre">Dict</span><span class="p"><span class="pre">[</span></span><span class="pre">Tuple</span><span class="p"><span class="pre">[</span></span><span class="pre">str</span><span class="p"><span class="pre">,</span> </span><span class="pre">str</span><span class="p"><span class="pre">]</span></span><span class="p"><span class="pre">,</span> </span><span class="pre">float</span><span class="p"><span class="pre">]</span></span></em><a class="headerlink" href="#mgrid.power_flow.snapshot.Snapshot.increments" title="Permalink to this definition">¶</a></dt>
+<dd><p>incremental values of conversion elements with respect to
+the previous snapshot</p>
+</dd></dl>
+
+<dl class="py attribute">
+<dt id="mgrid.power_flow.snapshot.Snapshot.previous">
+<code class="sig-name descname"><span class="pre">previous</span></code><em class="property"><span class="pre">:</span> <span class="pre">Union</span><span class="p"><span class="pre">[</span></span><a class="reference internal" href="grid.html#mgrid.grid.geographic.GeoGrid" title="mgrid.grid.geographic.GeoGrid"><span class="pre">mgrid.grid.geographic.GeoGrid</span></a><span class="p"><span class="pre">,</span> </span><a class="reference internal" href="#mgrid.power_flow.snapshot.Snapshot" title="mgrid.power_flow.snapshot.Snapshot"><span class="pre">mgrid.power_flow.snapshot.Snapshot</span></a><span class="p"><span class="pre">,</span> </span><a class="reference internal" href="grid.html#mgrid.grid.supra.SupraGrid" title="mgrid.grid.supra.SupraGrid"><span class="pre">mgrid.grid.supra.SupraGrid</span></a><span class="p"><span class="pre">]</span></span></em><a class="headerlink" href="#mgrid.power_flow.snapshot.Snapshot.previous" title="Permalink to this definition">¶</a></dt>
+<dd><p>previous snapshot</p>
+</dd></dl>
+
+<dl class="py method">
+<dt id="mgrid.power_flow.snapshot.Snapshot.result_pandapower">
+<code class="sig-name descname"><span class="pre">result_pandapower</span></code><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">net</span></span></em><span class="sig-paren">)</span><a class="reference internal" href="_modules/mgrid/power_flow/snapshot.html#Snapshot.result_pandapower"><span class="viewcode-link"><span class="pre">[source]</span></span></a><a class="headerlink" href="#mgrid.power_flow.snapshot.Snapshot.result_pandapower" title="Permalink to this definition">¶</a></dt>
+<dd><p>Get results from a <code class="docutils literal notranslate"><span class="pre">pandapower</span></code> model.</p>
+<dl class="field-list simple">
+<dt class="field-odd">Parameters</dt>
+<dd class="field-odd"><p><strong>net</strong> – a grid modelled using <code class="docutils literal notranslate"><span class="pre">pandapower</span></code>.</p>
+</dd>
+</dl>
+</dd></dl>
+
+<dl class="py method">
+<dt id="mgrid.power_flow.snapshot.Snapshot.result_pypsa">
+<code class="sig-name descname"><span class="pre">result_pypsa</span></code><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">net</span></span></em><span class="sig-paren">)</span><a class="reference internal" href="_modules/mgrid/power_flow/snapshot.html#Snapshot.result_pypsa"><span class="viewcode-link"><span class="pre">[source]</span></span></a><a class="headerlink" href="#mgrid.power_flow.snapshot.Snapshot.result_pypsa" title="Permalink to this definition">¶</a></dt>
+<dd><p>Get results from a <code class="docutils literal notranslate"><span class="pre">pypsa</span></code> model.</p>
+<dl class="field-list simple">
+<dt class="field-odd">Parameters</dt>
+<dd class="field-odd"><p><strong>net</strong> – a grid modelled using <code class="docutils literal notranslate"><span class="pre">pypsa</span></code>.</p>
+</dd>
+</dl>
+</dd></dl>
+
+<dl class="py method">
+<dt id="mgrid.power_flow.snapshot.Snapshot.update_previsou">
+<code class="sig-name descname"><span class="pre">update_previsou</span></code><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">previous</span></span></em><span class="sig-paren">)</span><a class="reference internal" href="_modules/mgrid/power_flow/snapshot.html#Snapshot.update_previsou"><span class="viewcode-link"><span class="pre">[source]</span></span></a><a class="headerlink" href="#mgrid.power_flow.snapshot.Snapshot.update_previsou" title="Permalink to this definition">¶</a></dt>
+<dd><p>Update items with respect to given previous snapshost.</p>
+<dl class="field-list simple">
+<dt class="field-odd">Parameters</dt>
+<dd class="field-odd"><p><strong>previous</strong> (<a class="reference internal" href="#mgrid.power_flow.snapshot.Snapshot" title="mgrid.power_flow.snapshot.Snapshot"><code class="xref py py-class docutils literal notranslate"><span class="pre">Snapshot</span></code></a>) – another snapshot used as previous reference.</p>
+</dd>
+</dl>
+</dd></dl>
+
+<dl class="py attribute">
+<dt id="mgrid.power_flow.snapshot.Snapshot.voltages">
+<code class="sig-name descname"><span class="pre">voltages</span></code><em class="property"><span class="pre">:</span> <span class="pre">Optional</span><span class="p"><span class="pre">[</span></span><span class="pre">pandas.core.frame.DataFrame</span><span class="p"><span class="pre">]</span></span></em><em class="property"> <span class="pre">=</span> <span class="pre">None</span></em><a class="headerlink" href="#mgrid.power_flow.snapshot.Snapshot.voltages" title="Permalink to this definition">¶</a></dt>
+<dd><p>votlage at buses in kVA</p>
+</dd></dl>
+
+</dd></dl>
+
+<div class="section" id="module-mgrid.power_flow.series">
+<span id="snapshot-series"></span><h2>Snapshot Series<a class="headerlink" href="#module-mgrid.power_flow.series" title="Permalink to this headline">¶</a></h2>
+<p>Class for building a series of snapshots.</p>
+<p>A <code class="docutils literal notranslate"><span class="pre">GeoGrid</span></code> or <code class="docutils literal notranslate"><span class="pre">SupraGrid</span></code> object will serve as the default snapshot.
+Increments at some snapshot will be stored in <code class="docutils literal notranslate"><span class="pre">Snapshot</span></code> object.</p>
+<p>The input and result of power flow calculation are stored in the same
+instance. There are two kinds of results, voltages and flows.</p>
+<dl class="py class">
+<dt id="mgrid.power_flow.series.SnapshotSeries">
+<em class="property"><span class="pre">class</span> </em><code class="sig-prename descclassname"><span class="pre">mgrid.power_flow.series.</span></code><code class="sig-name descname"><span class="pre">SnapshotSeries</span></code><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">iterable</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">()</span></span></em>, <em class="sig-param"><span class="o"><span class="pre">/</span></span></em><span class="sig-paren">)</span><a class="reference internal" href="_modules/mgrid/power_flow/series.html#SnapshotSeries"><span class="viewcode-link"><span class="pre">[source]</span></span></a><a class="headerlink" href="#mgrid.power_flow.series.SnapshotSeries" title="Permalink to this definition">¶</a></dt>
+<dd><p>Bases: <code class="xref py py-class docutils literal notranslate"><span class="pre">list</span></code></p>
+<dl class="py method">
+<dt id="mgrid.power_flow.series.SnapshotSeries.add_series">
+<code class="sig-name descname"><span class="pre">add_series</span></code><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">attribute</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">values</span></span></em><span class="sig-paren">)</span><a class="reference internal" href="_modules/mgrid/power_flow/series.html#SnapshotSeries.add_series"><span class="viewcode-link"><span class="pre">[source]</span></span></a><a class="headerlink" href="#mgrid.power_flow.series.SnapshotSeries.add_series" title="Permalink to this definition">¶</a></dt>
+<dd></dd></dl>
+
+<dl class="py method">
+<dt id="mgrid.power_flow.series.SnapshotSeries.add_snapshot">
+<code class="sig-name descname"><span class="pre">add_snapshot</span></code><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">time</span></span></em><span class="sig-paren">)</span><a class="reference internal" href="_modules/mgrid/power_flow/series.html#SnapshotSeries.add_snapshot"><span class="viewcode-link"><span class="pre">[source]</span></span></a><a class="headerlink" href="#mgrid.power_flow.series.SnapshotSeries.add_snapshot" title="Permalink to this definition">¶</a></dt>
+<dd></dd></dl>
+
+<dl class="py method">
+<dt id="mgrid.power_flow.series.SnapshotSeries.get_series">
+<code class="sig-name descname"><span class="pre">get_series</span></code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="reference internal" href="_modules/mgrid/power_flow/series.html#SnapshotSeries.get_series"><span class="viewcode-link"><span class="pre">[source]</span></span></a><a class="headerlink" href="#mgrid.power_flow.series.SnapshotSeries.get_series" title="Permalink to this definition">¶</a></dt>
+<dd></dd></dl>
+
+</dd></dl>
+
+</div>
+</div>
+
+
+           </div>
+
+          </div>
+          <footer>
+    <div class="rst-footer-buttons" role="navigation" aria-label="footer navigation">
+        <a href="bibliography.html" class="btn btn-neutral float-right" title="Bibliography" accesskey="n" rel="next">Next <span class="fa fa-arrow-circle-right" aria-hidden="true"></span></a>
+        <a href="power_flow.html" class="btn btn-neutral float-left" title="Power Flow Calculation" accesskey="p" rel="prev"><span class="fa fa-arrow-circle-left" aria-hidden="true"></span> Previous</a>
+    </div>
+
+  <hr/>
+
+  <div role="contentinfo">
+    <p>
+        &#169; Copyright 2020-2021, Edward Xu.
+
+    </p>
+  </div>
+
+
+
+    Built with <a href="https://www.sphinx-doc.org/">Sphinx</a> using a
+
+    <a href="https://github.com/readthedocs/sphinx_rtd_theme">theme</a>
+
+    provided by <a href="https://readthedocs.org">Read the Docs</a>.
+
+</footer>
+        </div>
+      </div>
+
+    </section>
+
+  </div>
+
+
+  <script type="text/javascript">
+      jQuery(function () {
+          SphinxRtdTheme.Navigation.enable(true);
+      });
+  </script>
+
+
+
+
+
+
+</body>
+</html>
\ No newline at end of file
diff --git a/docs/transformation.html b/docs/transformation.html
index 844a87f..5630c8a 100644
--- a/docs/transformation.html
+++ b/docs/transformation.html
@@ -38,8 +38,8 @@
 
     <link rel="index" title="Index" href="genindex.html" />
     <link rel="search" title="Search" href="search.html" />
-    <link rel="next" title="Bibliography" href="bibliography.html" />
-    <link rel="prev" title="Power Flow Calculation" href="power_flow.html" />
+    <link rel="next" title="Power Flow Calculation" href="power_flow.html" />
+    <link rel="prev" title="Power Grid" href="grid.html" />
 </head>
 
 <body class="wy-body-for-nav">
@@ -91,8 +91,9 @@
               <ul class="current">
 <li class="toctree-l1"><a class="reference internal" href="graph.html">Graph Theoretic Model</a></li>
 <li class="toctree-l1"><a class="reference internal" href="grid.html">Power Grid</a></li>
-<li class="toctree-l1"><a class="reference internal" href="power_flow.html">Power Flow Calculation</a></li>
 <li class="toctree-l1 current"><a class="current reference internal" href="#">Transformation</a></li>
+<li class="toctree-l1"><a class="reference internal" href="power_flow.html">Power Flow Calculation</a></li>
+<li class="toctree-l1"><a class="reference internal" href="snapshots.html">Snapshot</a></li>
 </ul>
 <ul>
 <li class="toctree-l1"><a class="reference internal" href="bibliography.html">Bibliography</a></li>
@@ -165,14 +166,14 @@
 
   <div class="section" id="module-mgrid.transformation">
 <span id="transformation"></span><h1>Transformation<a class="headerlink" href="#module-mgrid.transformation" title="Permalink to this headline">¶</a></h1>
-<p>Function to transform multilayer network from one format to another.</p>
+<p>Function to convert planar graph to supra graph.</p>
 <dl class="py function">
 <dt id="mgrid.transformation.planar2supra">
 <code class="sig-prename descclassname"><span class="pre">mgrid.transformation.</span></code><code class="sig-name descname"><span class="pre">planar2supra</span></code><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">g</span></span></em><span class="sig-paren">)</span><a class="reference internal" href="_modules/mgrid/transformation.html#planar2supra"><span class="viewcode-link"><span class="pre">[source]</span></span></a><a class="headerlink" href="#mgrid.transformation.planar2supra" title="Permalink to this definition">¶</a></dt>
 <dd><p>Convert a planar grid to corresponding supra-grid.</p>
 <dl class="field-list simple">
 <dt class="field-odd">Parameters</dt>
-<dd class="field-odd"><p><strong>g</strong> (<code class="xref py py-data docutils literal notranslate"><span class="pre">Union</span></code>[<a class="reference internal" href="graph.html#mgrid.graph.planar.PlanarGraph" title="mgrid.graph.planar.PlanarGraph"><code class="xref py py-class docutils literal notranslate"><span class="pre">PlanarGraph</span></code></a>, <a class="reference internal" href="grid.html#mgrid.grid.planar.PlanarGrid" title="mgrid.grid.planar.PlanarGrid"><code class="xref py py-class docutils literal notranslate"><span class="pre">PlanarGrid</span></code></a>]) – a planar graph or grid to be converted.</p>
+<dd class="field-odd"><p><strong>g</strong> (<code class="xref py py-data docutils literal notranslate"><span class="pre">Union</span></code>[<a class="reference internal" href="graph.html#mgrid.graph.geographic.GeoGraph" title="mgrid.graph.geographic.GeoGraph"><code class="xref py py-class docutils literal notranslate"><span class="pre">GeoGraph</span></code></a>, <a class="reference internal" href="grid.html#mgrid.grid.geographic.GeoGrid" title="mgrid.grid.geographic.GeoGrid"><code class="xref py py-class docutils literal notranslate"><span class="pre">GeoGrid</span></code></a>]) – a planar graph or grid to be converted.</p>
 </dd>
 <dt class="field-even">Return type</dt>
 <dd class="field-even"><p><a class="reference internal" href="grid.html#mgrid.grid.supra.SupraGrid" title="mgrid.grid.supra.SupraGrid"><code class="xref py py-class docutils literal notranslate"><span class="pre">SupraGrid</span></code></a></p>
@@ -191,8 +192,8 @@
           </div>
           <footer>
     <div class="rst-footer-buttons" role="navigation" aria-label="footer navigation">
-        <a href="bibliography.html" class="btn btn-neutral float-right" title="Bibliography" accesskey="n" rel="next">Next <span class="fa fa-arrow-circle-right" aria-hidden="true"></span></a>
-        <a href="power_flow.html" class="btn btn-neutral float-left" title="Power Flow Calculation" accesskey="p" rel="prev"><span class="fa fa-arrow-circle-left" aria-hidden="true"></span> Previous</a>
+        <a href="power_flow.html" class="btn btn-neutral float-right" title="Power Flow Calculation" accesskey="n" rel="next">Next <span class="fa fa-arrow-circle-right" aria-hidden="true"></span></a>
+        <a href="grid.html" class="btn btn-neutral float-left" title="Power Grid" accesskey="p" rel="prev"><span class="fa fa-arrow-circle-left" aria-hidden="true"></span> Previous</a>
     </div>
 
   <hr/>
diff --git a/docs_raw/graph.rst b/docs_raw/graph.rst
index c7c56a5..7587fb4 100644
--- a/docs_raw/graph.rst
+++ b/docs_raw/graph.rst
@@ -1,10 +1,10 @@
 Graph Theoretic Model
 =====================
 
-Planar Graph
-------------
+Geographic Graph
+----------------
 
-.. automodule:: mgrid.graph.planar
+.. automodule:: mgrid.graph.geographic
    :members:
    :undoc-members:
    :show-inheritance:
diff --git a/docs_raw/grid.rst b/docs_raw/grid.rst
index 1283b05..43c99e2 100644
--- a/docs_raw/grid.rst
+++ b/docs_raw/grid.rst
@@ -1,10 +1,10 @@
 Power Grid
 ==========
 
-as Planar Graph
----------------
+as Geographic Graph
+-------------------
 
-.. automodule:: mgrid.grid.planar
+.. automodule:: mgrid.grid.geographic
    :members:
    :undoc-members:
    :show-inheritance:
diff --git a/docs_raw/index.rst b/docs_raw/index.rst
index 069e437..fdca045 100644
--- a/docs_raw/index.rst
+++ b/docs_raw/index.rst
@@ -112,8 +112,9 @@ API
 
    graph
    grid
-   power_flow
    transformation
+   power_flow
+   snapshots
 
 Bibliography
 ------------
diff --git a/docs_raw/snapshots.rst b/docs_raw/snapshots.rst
new file mode 100644
index 0000000..79acb2e
--- /dev/null
+++ b/docs_raw/snapshots.rst
@@ -0,0 +1,15 @@
+Snapshot
+========
+
+.. automodule:: mgrid.power_flow.snapshot
+   :members:
+   :undoc-members:
+   :show-inheritance:
+
+Snapshot Series
+---------------
+
+.. automodule:: mgrid.power_flow.series
+   :members:
+   :undoc-members:
+   :show-inheritance:
diff --git a/mgrid/__init__.py b/mgrid/__init__.py
index 1320cd9..22578df 100644
--- a/mgrid/__init__.py
+++ b/mgrid/__init__.py
@@ -8,4 +8,4 @@
   network, or network of networks for sure.
 
 """
-__version__ = "0.2.6"
+__version__ = "0.2.7"
diff --git a/pyproject.toml b/pyproject.toml
index 54fabc5..7367ff1 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,6 +1,6 @@
 [tool.poetry]
 name = "mgrid"
-version = "0.2.6"
+version = "0.2.7"
 description = "power grid with multiple voltage levels as multilayer network"
 authors = ["Edward Xu <edxu96@outlook.com>"]
 
@@ -23,6 +23,7 @@ docutils = "^0.16"
 darglint = "^1.5.8"
 black = "^20.8b1"
 pre-commit = "^2.9.3"
+setuptools = "53.0.0"
 
 [tool.black]
 line-length = 79
diff --git a/setup.py b/setup.py
new file mode 100644
index 0000000..a217fc0
--- /dev/null
+++ b/setup.py
@@ -0,0 +1,9 @@
+"""Set up current package.
+
+Remember to put ``pyproject.toml`` in another directory before editable
+install, see https://stackoverflow.com/a/65787633/10181743.
+"""
+import setuptools
+
+if __name__ == "__main__":
+    setuptools.setup()