Jenks natural breaks classification method
Data in the state maps are categorized using a modification of the Jenks natural breaks classification method. The Jenks method clusters data into groups that minimize the within-group variance and maximize the between-group variance. The modification rounds the data cut points to assist map reading by a general audience. For more information, see: Brewer CA, Pickle L. Evaluation of methods for classifying epidemiological data on choropleth maps in series. Ann Assoc Am Geogr 92(4):662–81. 2003.