Standardized Choropleth Map

http://www.cdc.gov/copd/data.htm
Standardized choropleth maps, like this one showing the age-standardized death rate for chronic obstructive pulmonary disease are very useful due to the equal distribution over the population to show the variables significance across the country without skewing the results due to inequality of population density in certain states. Shading is then used to show prevalence of the variable across the state holding dependent variables more constant.