mojchart

mojchart is an R package that provides custom formatting for charts in ggplot2. It includes a theme function based on Government Analysis Function guidance and colour palettes based on Analysis Function guidance and MoJ corporate branding (MoJ internal link).

Installation

You can install mojchart with:

install.packages("devtools")
devtools::install_github("moj-analytical-services/mojchart")

Overview

The package provides a custom ggplot2 theme function, theme_gss(), which is based on guidance from the Government Statistical Service and Government Analysis Function.

The package also provides colour palettes that can be added using the custom scale functions scale_colour_moj() and scale_fill_moj(). The colour palettes can also be returned as hex codes using moj_palette(). Each palette contains six colours.

Theme function

The theme function theme_gss() is based on Analysis Function guidance (Data visualisation:charts). It aims to minimise unnecessary visual elements and to assist with label positioning. The theme allows for a main title, plus a subtitle for statistical details. The data source can be shown in the caption below the chart. To keep axis labels horizontal, theme_gss() suppresses the ggplot2 y axis label; a label can instead be included within the ggplot2 subtitle if required (see example 2 below).

theme_gss() includes a parameter to show or hide the x axis label, a parameter to show or hide the x axis tick marks, and a parameter to reverse the formatting of the x and y axes for use with coord_flip().

Colour palettes

The package provides three colour palettes taken from the Analysis Function guidance Data visualisation: colours (for categorical data, sequential data and “focus charts”) and five colour palettes based on MoJ corporate colours. There are six colours in each palette, but note that the Analysis Function guidance on the use of colour advises using no more than four categories for line charts and clustered or stacked bar charts.

The Analysis Function colour palettes have been designed around current accessibility requirements. The colour palettes based on MoJ colours do not meet current accessibility requirements for contrast ratios.

For MoJ corporate colours, there are two types of colour scheme: vibrant and muted. The vibrant schemes use MoJ corporate colours directly. The muted schemes are based on MoJ colours but with reduced saturation. Reduced saturation was previously recommended in Government Statistical Service guidance for shading areas, such as for bar charts.

For sequential colour palettes or continuous data, you could look at the inbuilt ggplot2 options, or try the colorspace package.

Running palette_names() returns the colour palette names.

library(mojchart)
palette_names()
#> [1] "muted1"        "muted2"        "muted3"        "vibrant1"     
#> [5] "vibrant2"      "govanal_bars"  "govanal_lines"

You can use scale_colour_moj() or scale_fill_moj() to apply a colour palette to a ggplot2 chart, passing the number of colours and the name of a colour palette as arguments. There is an optional order parameter to change the colour order.

To obtain a sequence of colours as a vector, use moj_palette(), again specifying the number of colours and the name of a colour palette. The display_colours() function displays the sequence of colours.

pal <- moj_palette(n = 5, palette = "muted3")
pal
#> mojdarkblue    midblue1       teal2       pink1     yellow1 
#>   "#003057"   "#3975ac"   "#59a6a4"   "#f3bee0"   "#feebb3"

display_colours(pal)

All of the colour sequences available within each colour palette are shown here.

Accessing individual colours

moj_colours() provides the hex codes for all MoJ corporate colours. govanal_colours() provides the Government Analysis Function colours. palette_colours() provides all colours used in the mojchart colour palettes. Running one of these functions with no arguments returns a vector containing all of the available colours. Passing the names of individual colours returns just those.

moj_colours("mojblue", "mojgreen")
#>   mojblue  mojgreen 
#> "#1d609d" "#30aa51"

Accessibility

See the Analysis Function guidance for a full discussion of accessibility considerations regarding the use of colour in charts.

In general, accessibility decreases as you use more colours.

Of the colour palettes in this package, only the Analysis Function palettes have been checked for contrast ratios that meet accessibility requirements.

All of the colour palettes aim to be accessible to those with the most common forms of colour blindness.

Below are two resources to help assess colour blindness accessibility.

• To simulate how an image file could appear to individuals with forms of colour blindness:
  https://www.color-blindness.com/coblis-color-blindness-simulator/
• To simulate the appearance of a colour palette of hex codes:
  https://davidmathlogic.com/colorblind/

Note that for line charts, the Analysis Function guidance recommends labelling lines directly rather than using a separate legend. The directlabels package provides one way to implement this in R.

Examples

The examples below show the use of theme_gss(), scale_colour_moj() and scale_fill_moj(), together with various ggplot2 functions, to create fully formatted charts. The data frames for the charts are produced by two mojchart functions, familystarts_reduced() and bars().

Example 1: line chart

• In this example note that the line thickness has been increased in geom_line() so that the colours stand out more, making the categories easier to identify.

library(mojchart)
library(ggplot2)

ggplot(familystarts_reduced(6), aes(x = year_qtr, y = count, colour = case_type)) +
  geom_line(linewidth = 1.5) +
  labs(title = "Number of cases started in family courts",
       subtitle = "England and Wales, Q1 2011 - Q2 2020",
       caption = "Source: Family court statistics quarterly, April to June 2020 (table 1)") +
  scale_y_continuous(expand = expansion(mult = c(0, 0.05)), label = scales::label_comma()) +
  zoo::scale_x_yearqtr(labels = scales::label_date("%Y-Q%q")) +
  expand_limits(y = 0) +
  theme_gss(xticks = TRUE) +
  scale_colour_moj(6, palette = "govanal_lines", order = c(1, 3, 2, 6, 4, 5))

Example 2: grouped bar chart

ggplot(bars(4), aes(x = col1, y = col3, fill = col2)) +
  geom_col(position = position_dodge2(padding = 0.2), width = 0.8) +
  labs(title = "Example grouped bar chart",
       subtitle = "Additional details here\n\nAxis label",
       caption = "Source") +
  scale_y_continuous(expand = expansion(mult = c(0, 0.05))) +
  expand_limits(y = 10) +
  theme_gss() +
  scale_fill_moj(4, palette = "muted2")

Example 3: horizontal bar chart

ggplot(bars(3), aes(x = col1, y = col3, fill = col2)) +
  geom_col(position = "dodge2", width = 0.8) +
  coord_flip() +
  labs(title = "Example horizontal bar chart",
       subtitle = "Additional details here\n",
       caption = "Source",
       y = "Axis label") +
  scale_y_continuous(expand = expansion(mult = c(0, 0.05))) +
  expand_limits(y = 10) +
  guides(fill = guide_legend(reverse = TRUE)) +
  theme_gss(flipped = TRUE, xlabel = TRUE) +
  scale_fill_moj(3, palette = "govanal_bars")