Choropleth map

http://www.agcensus.usda.gov/Publications/2002/Ag_Atlas_Maps/Crops_and_Plants/Hay_and_Forage_Crops_Harvested/Hay%20-%20All%20Hay%20Including%20Alfalfa,%20Other%20Tame,%20Small%20Grain-choropleth%20map.gif

A Cholorpleth map is a map that uses color to portray whatever variable it is describing. This map is describing acres used for hay protection in 2002. This map is a choropleth map because of its use of the different shades of green to portray the data of this map.