Bivariate Choropleth Map

Bivariate Choropleth Maps show two different variables on one map by using colors, shading, symbols, or patterns. Generally, lines are used to show the second variable; whether they are vertical, horizontal, angular lines and/or colored. Shading is usually used for the main/base information.

The map shown is a Bivariate Choropleth Map of "Percent Change, 1990 to 2000 and Population Density, 1990." The different colors show the 3 ranges of people per square mile in 1990. The lighter to darker shading represent the population change from a loss to unnumbered gain.

http://www.personal.psu.edu/cab38/GEOG321/14_multivariate02/multivariate.html