Choropleth Map

http://politicalmaps.org/

Choropleth maps are shaded or proportioned to show a statistic. In the map above, states are shaded based on their popular vote for the 2012 presidential election. Choropleth maps are a quick tool to asses and present a measured variable across a large span of geography. Some choropleth maps have only 2 colors, like the example above, but other choropleth maps may be shaded from dark to light or even distort land figures to present data.