Bivariate Choropleth Map

http://proceedings.esri.com/library/userconf/proc99/proceed/papers/pap171/p171.htm

Bivariate mapping displays two variables on a single map by combining the two different sets of graphic symbols. This map displays both the data of the population of 1997 and the data of the median house value in that time. This map has no consistent findings because in some areas it seems that higher population leads to a higher median house value and in other it does not indicate that.