Univariate choropleth map - Percentage of people in poverty in the U.S.

http://www.citylab.com/work/2011/12/americas-new-poverty-belt/677/ 

A Univariate choropleth map means that only one type of data is being examined and displayed on the map.  This map, like many choropleth maps, uses varying values (or lightness/darkness of shading) of the hue (in this case blue) to differentiate between the different interval steps.  We can see from this map that from 2006 to 2010, the states with the largest percentage of people living in poverty areas are in the southern/central part of the U.S. (from New Mexico to Alabama and up through Kentucky).