choropleth map

n.A map that uses shades or colors to indicate some attribute of given regions on a map.

Notes

Choropleth maps are often used for political districts (counties, wards, census tracts), with a different color used to indicate the data value for the area. For example, a map of voting precincts might be colored red or blue to indicate which party won an election. A map of census tracts might use shades of a color to indicate population density. A choropleth map differs from an isolpeth map in that in the latter the regions are defined by some quality other than the data itself.