Univariate Choropleth Map

http://www.colocarto.com/custom-thematic-maps.html

Above is an Univariate Choropleth Map, this map type is useful for portraying data that is derived from one variable.  This map is still considered a choropleth map by all underlying factors, but the biggest attribute that differentiates it from other choropleths is that it only represents one variable. The map above shows the estimated median household income for the contiguous United States in 2008.