Bivariate Choropleth maps

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

This map is a Bivariate choropleth map becasue it shows two data sets which are the winter vs summer Olympic athletes per capita. This map shows the highest and lowest density of summer and winter athletes in the country.