Bivariate Choropleth Map

http://www.directionsmag.com/articles/sports-illustrated-from-swimsuits-to-maps-the-making-of-the-si-sports-atlas/123556

A bivariate choropleth map is a choropleth map that represents more than one variable. In this map, the color key has two axis that represent two different variables. Then the colors line up with each variable to tell how much of each.