After the election, I was curious how much population density had to do with party affiliation. Behind the cut is a graph that somewhat speaks to that question. The graph is the number of ballots cast in a given county versus the percentage of the popular vote the candidates received. It's not quite population density. I didn't have a handy list of the land areas of the counties.
The graph is smoothed a great deal. Without the smoothing, the center section has too much noise to sort out entirely. Most of the 4500+ counties in the country fall fairly close to the center of this graph.
The data for the voting by county was plucked from the CNN pages. There are a variety of counties where not all (or even 'any') of the precincts have reported yet. So, the graph is slightly incomplete. If CNN ever gets these pages up to 100%, then I'll regenerate the graph.