Topical thread Feb.3 2010 Pop. density and idealogy

reader sammy submits this question:

Population Density and Ideology

Sammy compared the famous Red/Blue electoral map (by county) with a map of Population Density

and found pretty strong correlation. Areas with high population density vote Democratic, while areas with low population density vote Republican.

What, if anything, explains this correlation?

Sammy’s theory is:

1) People living in high-density areas have a stronger need for government services and control, as everyone’s actions have a greater effect on others, simply du to proximity. This need/desire expresses itself by pulling the (D) lever.

2) Higher population densities result in stronger peer pressure, which enhances a (D) majority.
Before you offer your own theory,  you might want to test it against the exit polls here.

(My own thought is in comments)