Classed Choropleth Map

Classed Choropleth Maps are maps that use specific ranges or classes that are used to help classify aerial units. These types of maps can be compared to Range Graded Proportional Circle Maps because they both have a set number of ranges. The difference between the two is Classed Choropleth Maps use shading, colors, and patterns of aerial units versus varying circle sizes. Counties are commonly used as an aerial unit. There are four classes: equal steps, quantiles, natural breaks, and minimum variance.

The map shown is a Classed Choropleth map of the "Percent English, 2000." It is a Classed map because colors are attributed to arbitrary ranges that were determined by one of the four classing systems. The darker the color, the higher the percentage of people with English heritage; the lighter the color the lower, the percentage of people with English heritage.

http://blogreadersblog.blogspot.com/2008/11/americans-with-english-ancestry-vote.html