There are several methods for automatic classification. One common method is called which subtracts the lowest value of the classification variable from the highest value, and defines equal$-$width boundaries to fir the desired number of classes into the range.

Another common method is the classification, which can lead to a visually balanced map because all classes have approximately equal extents.

An alternative to this approach is to identify naturally occurring clusters of data based on an ordering variable. This is known as classification.