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 isopleth map in that in the former the regions are predefined by some quality other than the data represented.
