Doing data visualization is kind of trendy these days but that doesn't mean it isn't fun. Here's something I whipped up that maps US counties by population density vs. % Democratic vote in the last election. Interactive version with map is here.
It's no surprise that denser areas (note the log scale) tend to vote more Democratic, although it was a bit startling how pronounced the correlation is. If you ignore the small smattering of low-density counties that went Democratic (and pretty much all of them are areas dominated by a racial minority) then it's almost perfect. One party represents urban cosmopolitans (that is, the civilized, which just means living in cities) and the other rural hicks.