Thematic Map
Thematic Maps show a specific theme or data pattern in the map. Statistically thematic maps specifically take statistics and turn them into maps using shading or dots to demonstrate the stats.
For a map showing population density, the statistics were likely taken from the Census Bureau and using shading created a map color coded by population numbers. The statistics were put into a thematic map to create a quick visual of the population of an area. Thematic maps help make statistics about the demographics of an area easier to view because of the visual statement the map makes compared to a list of numbers.