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Data classification, also known as data classing or selection of intervals, is the process by which a set of interval or ratio data are divided into a small number of classes or categories. Such classification is necessary for the construction of classed choropleth maps in which a range of different colors or shadings is used to depict the set of data classes. The selection of intervals so strongly influences the apparent information content of a map that knowing how to choose appropriate class intervals is a necessary skill for any GIS user.

Number of Classes

While there is some disagreement as to the precise number, there is general agreement that human cognition limits our ability to visually discriminate more than 10 or 11 different colors or tint ...

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