A choropleth map fills geographic regions—such as counties, states, or countries—with colors or shades that encode data values. It is popular and easy to make, but color can accidentally make land area look more important than the people or events being measured. section 6.3.1
The election-map trap
A county map colored only by the 2016 US presidential election winner creates a sea of red, suggesting overwhelming support. Coloring counties by the winning candidate’s vote percentage adds detail, but still leaves large rural areas visually dominant. Population, not acreage, determined the popular vote. section 6.3.1
Use a choropleth carefully:
- Choose it when the data genuinely concerns land, such as farmland, public parks, or residential use. section 6.3.1
