Classed choropleth maps are choropleth maps in which areal units are combined into a smaller number of groups and portrayed in intervals. Classification techniques include equal steps, quantiles, natural breaks and minimum variance.The map above shows a region which has experienced varying population changes and is represented by five intervals. The data is equally spread out among those intervals meaning that since there are 67 counties, and 5 intervals, then each interval contains a little bit above 13 counties (on average). This is the quantile classification method. However, an aspect that is misleading about this is that each county might belong to the same interval, but have huge differences in actual percent population change since the data might have jumps within intervals (and while the amount of of data is equal in each interval, the range of each interval is not).
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