Classed Chloropleth Maps

In a classed chloropleth map the variables of data are combined into groups. These groups are then portrayed in intervals. A classed chloropleth map is best designed using four to seven intervals. The intervals can be divided up using the techniques of equal steps, quantiles, natural breaks, or minimum variance. The picture above shows a classed chloropleth map of the United States water usage. The different shades of blue represent the five different intervals of range of use. This classed chloropleth map is most likely an equal step classification, due to the fact that the total range is divided into categories which were most likely designed by the map designer. The drawbacks in the map can be seen with the amount of states in each category. The top category only has three states where the 2,000 to 5,000 million gallons per day category contains 19 states.

http://ga.water.usgs.gov/edu/wateruse2000.html