Automatic reclassification

User-controlled classifications require a classification table or user interaction. GIS software can also perform automatic classification, in which a user only specifies the number of classes in the output data set. The system automatically determines the class break points. The two main techniques of determining break points being used are the equal interval technique and the equal frequency technique.

Equal Interval Technique

The minimum and maximum values v_min and v_max of the classification parameter are determined and the (constant) interval size for each category is calculated as (v_max - v_min) ∕ n, where n is the number of classes chosen by the user. This classification is useful in that it reveals the distribution pattern, as it determines the number of features in each category.

Equal Frequency Technique

This technique is also known as quantile classification. The objective is to create categories with roughly equal numbers of features per category. The total number of features is determined first, then, based on the required number of categories, the number of features per category is calculated. The class break points are then determined by counting off the features in order of classification parameter value.