I had an impulse to visualize the common intuition that progressive politics is correlated with population density. This was the result.

Each circle in the scatterplot is a county.
Size represents population; color represents degree of Republican-leaning (red) vs Demicratic-leaning (blue) votes in the 2012 presidential election.
The x-axis of the scatterplot is the population density (people/km2) on a log scale.
The y-axis is % of the vote that went Democratic in the 2012 presidential election.
Try selecting a region in the scatterplot or map.

Data Sources: election results from Politico; county density from Freebase

Made with D3 by Mike Travers. Source.