Predominance
What is a predominance style?
A predominance style colors features based on the category with the highest (or predominant) number among a set of similar categories. You can use this style to map anything that involves sub-categories of a larger population.
- The winner of an election
- The predominant language spoken at home
- The most common race/ethnicity in a region
How a predominance style works
This style requires writing an Arcade expression that returns the category with the largest number. The following expression returns a string for the predominant educational attainment level for a given feature.
Once the expression is authored, create a unique value renderer and set the following:
- Reference the Arcade expression in the
valueExpression
property. - Create unique value info objects for each of the expected values returned from the expression.
Examples
Predominant value
The following example colors each census tract based on the predominant educational attainment of adults age 25 years or older.
Predominance with opacity
In a predominance visualization, the color representing the predominant value will shade the whole polygon with the same opacity and saturation as any neighboring polygon even if the predominant value wins over other values by the slimmest margin.
Adding an opacity variable helps emphasize strong predominant values and wash out features where the predominant value is relatively weak. The Arcade expression can return the margin between the predominant value and the second place value, or it can be simpler and return the share of the predominant value as a percentage of all values.
Predominance with size
Many times in demographic maps, large features represent areas with fewer people. In a predominance visualization, the colors of these large features can dominate the view, thus making them appear more influential or important than they actually are.
Adding a size variable that returns the sum of all categories considered in the predominance expression can help provide additional context to the user. This requires switching from a fill symbol to a marker symbol.
This is particularly important for election maps where relatively unimportant large areas dominate the view more than high population areas.
Tutorials

Style a feature layer
Use symbols and renderers to style feature layers.

Style layers in a web map
Use Map Viewer to style layers in a web map.
Services
Feature service
Add, update, delete, and query feature data.
API support
Different APIs have different levels of support for data-driven visualization.
Unique types | Class breaks | Visual variables | Time | Multivariate | Predominance | Dot density | Relationship | |
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ArcGIS API for JavaScript | ||||||||
ArcGIS Runtime API for Android | ||||||||
ArcGIS Runtime API for iOS | ||||||||
ArcGIS Runtime API for Java | ||||||||
ArcGIS Runtime API for .NET | ||||||||
ArcGIS Runtime API for Qt | ||||||||
ArcGIS API for Python |