Select a demographic variable to see its relationship to the winner of each county. Brighter colors reflect a higher demographic value (not margin of victory). About this kind of map >
The maps here use a technique called value-by-alpha, which is essentially a bivariate choropleth map that "equalizes" a base map so that the visual weight of a map unit corresponds to a data value. In this case, we are showing election results as a binary red-blue choropleth map, then varying visual weight by a demographic variable, fading out counties with low values. For example, in the population map counties with lower populations are less visually prominent while counties with high populations remain brightly colored, giving a more accurately weighted picture of the country than a map showing a sea of red in sparsely populated areas.
Value-by-alpha is something we experimented with following the 2008 presidential election as an alternative method to display what is often shown by cartograms. It is an attempt to provide similar visual equalization of the map while maintaining the geographic accuracy that cartograms must sacrifice. For more about value-by-alpha maps, see the 2010 paper by Robert Roth et al.