Creating Basic Choropleths With ArcGIS Pro
A choropleth is a type of map where areas are colored based on a single variable that describes some characteristic of those areas. Choropleths can be used to visualize both categorical and quantitative variables.
A commonly-seen choropleth in the USA is red-blue maps showing the predominance of political parties in presidential elections:
The following video shows how to create a choropleth using a categorical variable. This example uses the electoral college winners by state in the 2012 US presidential election. The data is provided as the Minn 2016 Electoral Data feature service from the University of Illinois ArcGIS Online organization that was originally sourced from the Associated Press via Politico. The data is also available for download as a GeoJSON file.
Create the MapCreate a new map and add the layer Modify the projection Modify the symbology and select the categorical variable you are going to map Choose colors for the categories Select a base map Adjust transparency
Create a Print Layout For a FigureNew print layout Add map frame properties - remove frame line Add a legend Remove all other values Background Layer name = Title Display = Black border White background border x/y gap 0.1 in background x/y gap 0.1 in Export to PNG 300 DPI Insert in a Word document Remove the service credit Package your project
Create a Print Layout For a Standalone MapAdd a legend Add a title, frame line, and marginalia Package your project
Choropleths can also be used to visualize quantitative variables. This example uses infant mortality data from the World Bank. The data is provided as the Minn 2020 World Bank Health Indicators feature service from the University of Illinois ArcGIS Online organization. The data is also available for download as a GeoJSON file.Create a new map and add the layer Modify the projection Modify the symbology and select the variable you are going to map Choose an appropriate classification method Choose colors for the categories Select a base map Adjust transparency Create a print layout for a figure Add a legend Give the layer a meaningful name Package your project Create a print layout for a standalone map Add a legend Add a title, frame line, and marginalia Title with the unit for the variable Package your project
What Story Are You Trying To Tell?
The stylistic choices that you make in creating a choropleth tell a story. While the art of map making (cartography) is rich and complex, the following are a few considerationg to keep in mind when creating a choropleth.
ArcGIS Pro provides a number of different ways of allocating different ranges of numbers to different numbers (classification methods). The choice of which method you should use depends both on the characteristics of the variable you are mapping as well as the story you are trying to tell:Jenks Natural Breaks Equal Interval Quantile Standard Deviation
Map Rates Rather Than Counts
Map of count of votes just maps highly populous areas
Bubble maps are more appropriate for counts