Univariate Choropleth Map

http://water.usgs.gov/edu/wudo.html

A univariate choropleth map shows statistical data aggregated over predefined regions with coloring or shading of these regions. Univariate choropleth maps assume a relatively even distribution of the measured phenomenon within each region. Depending on the map data of the univariate choropleth map there are differences in hue to indicate qualitative differences while differences in saturation or lightness are used to indicate quantitative differences. The image shown above is of a univariate choropleth map showing water usage across the United States where extensive use of water was shown by blue color saturation.