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Predominance

This expression returns the alias describing the predominant field from a set of competing number fields. For example, if a layer contains three fields for vote totals (e.g. Republican, Democrat, Other), you should specify the field name for each and assign it an alias to be returned by the expression.

Read the Creating a predominance visualization with Arcade blog post from the ArcGIS blog for more information.

Use cases

Calculating predominance is useful when you have several competing numeric fields, and you would like to indicate the highest count (or winner) among the fields. This is common in the visualization profile, but it may be used in the popup and labeling profiles as well. This could be used to visualize the winner of an election or the top results from a survey.

Workflow

Copy and paste the expression found in the expression template below to the Arcade editor in ArcGIS Online, the relevant location in ArcGIS Pro, or the relevant location in a custom app.

To configure the script to your layer, you must construct an array of objects referring to competing number field values. Then describe the field using the text of the alias property.

For example, in a layer representing U.S. counties containing voting data from the 2016 U.S. presidential election, you would replace this:

var fields = [
  { value: $feature.FIELD_NAME_1, alias: "DESCRIBE FIELD_NAME_1 HERE" },
  { value: $feature.FIELD_NAME_2, alias: "DESCRIBE FIELD_NAME_2 HERE" },

  // e.g. { value: $feature.REPUB_VOTES, alias: "Republican Candidate" }
  // ADD MORE FIELDS AS NECESSARY
];

With something like the following:

var fields = [
  { value: $feature.REPUBLICAN_VOTES, alias: "Trump" },
  { value: $feature.DEMOCRAT_VOTES, alias: "Clinton" },
  { value: $feature.OTHER_VOTES, alias: "Other" }
];

Expression Template

// The fields from which to calculate predominance.
// The `value` property must reference a field global variable
// OR an arcade expression that returns a number
// Replace the field names and aliases in ALL CAPS with
// the competing fields in your layer

var fields = [
  { value: $feature.FIELD_NAME_1, alias: "DESCRIBE FIELD_NAME_1 HERE" },
  { value: $feature.FIELD_NAME_2, alias: "DESCRIBE FIELD_NAME_2 HERE" },

  // e.g. { value: $feature.REPUB_VOTES, alias: "Republican Candidate" }
  // ADD MORE FIELDS AS NECESSARY
];

// Returns the predominant category as the alias
// defined in the fields array. If there is a tie,
// then both names are concatenated and used to
// indicate the tie

function getPredominantCategory(fieldsArray){
  var maxValue = -Infinity;
  var maxCategory = "";
  for(var k in fieldsArray){
    if(fieldsArray[k].value > maxValue){
      maxValue = fieldsArray[k].value;
      maxCategory = fieldsArray[k].alias;
    } else if (fieldsArray[k].value == maxValue){
      maxCategory = maxCategory + "/" + fieldsArray[k].alias;
    }
  }
  // totals should exceed zero in predominance visualizations
  return IIF(maxValue <= 0, "none", maxCategory);
}

getPredominantCategory(fields);

Example output

See this web map for examples of how to use this expression in ArcGIS Online.

predominance