Bivariate Choropleth Map

This map was taken from http://voices.washingtonpost.com/ezra-klein/2010/04/the_red_state_ripoff.html

This is a good example of a Bivariate Choropleth Map.  The thing that makes this a bivariate map is that there are only two variables in consideration in this map.  It implies that there is a dichotomy between the variables so an electoral map is a good example.