Choropleth Map

Choropleth maps portray quantitative data as colors showing the density, percent, average value, or quantity of a phenomenon within the boundary of a certain geographic area. Sequential colors (color gradients) indicate increasing positive/negative data values.


A Choropleth map is a type of thematic map in which areas are shaded in proportion to the measurement of the variable being displayed on the map. Some examples include population density or political affiliation. It provides an easy way to visualize how a measurement varies across a geographic area. It also shows the level of variable within a region.
The above choropleth map shows areas of increasing harvest amounts if hay. The darker colors indicate areas of larger hay harvesting.
http://www.nass.usda.gov/research/atlas02/Crops/Hay%20and%20Forage%20Crops%20Harvested/Hay%20-%20All%20Hay%20Including%20Alfalfa,%20Other%20Tame,%20Small%20Grain,%20and%20Wild,%20Harvested%20Acres-choropleth%20map.gif