Bivariate Choropleth Map

http://www.geo.unizh.ch/~annal/Choropleth%20maps.html

A bivariate map displays two variables on a single map by combining two different sets of graphic symbols or colors. This type of map portrays two separate phenomena that occur simultaneously. The main objective of a bivariate map is to find a simple method for accurately and graphically illustrating the relationship between two spatially distributed variables. The above map shows the relationship between the percentage of population under the age of 18 to the percentage of rural population.