The Equal Interval classing method assigns the same value range for each class. When you select the number of classes that you want for the data, the data are divided accordingly.
When data are divided using the Quantile method, units of measurement are divided equally among the classes based on rank.
The User Defined classing method allows users to select low and high values for each class. It is helpful when there are one or more data values of particular significance to you.
For more information and examples, go to the U.S. Census Bureau’s American Factfinder site: http://factfinder.census.gov/home/en/epss/tm_classes_methods.html.