Choropleth Map

http://images.google.com/imgres?imgurl=http://www.nass.usda.gov/research/atlas02/Crops/Hay%2520and%2520Forage%2520Crops%2520Harvested/Hay%2520-%2520All%2520Hay%2520Including%2520Alfalfa,%2520Other%2520Tame,%2520Small%2520Grain,%2520and%2520Wild,%2520Harvested%2520Acres-choropleth%2520map.gif&imgrefurl=http://www.nass.usda.gov/research/atlas02/index.html&usg=__GU_qGw1FtZsoUtL4VrAsyxSX1Oc=&h=612&w=792&sz=83&hl=en&start=2&tbnid=r--6ddjd8jE-dM:&tbnh=111&tbnw=143&prev=/images%3Fq%3Dchoropleth%2Bmaps%26gbv%3D2%26hl%3Den%26sa%3DX

Choropleth maps are maps of specifically defined areas such as states, counties or districts, and can give a wide variety of information depending on which type is used. There is a later post that will make more distinctions.

This choropleth map demonstrates the value of crops in specific areas as a portion of the total market value of crops sold in 2002. Important items to consider when creating or using choropleth maps incude the area or regions depicted (states, counties, districts, etc), whether they are areally averaged or not, and how the steps or classes are broken down (i.e. equal steps, quatiles, natural breaks or mininum variance.)