Political Self-segregation

Via Yglesias, Peter Orszag looks at where we choose to live as the main cause of polarization:

If redistricting isn’t the primary force behind polarization, what is? One crucial cause, as documented in “The Big Sort,” a path-breaking book by Bill Bishop and Robert Cushing, is increased residential segregation by political party. We are voluntarily separating ourselves into Republican and Democratic neighborhoods. Today’s media and blogosphere, which increasingly filter news according to their point of view, exacerbate and reinforce the effect.
Two maps (see accompanying maps: 1976 Election and 2008 Election), taken from a recent paper by James Thomson of the RAND Corp., show the U.S. broken down by county (county lines have also not been redistricted). The dark-shaded counties are those that have swung hard one way or another in a presidential election, and so are considered polarized, while the light counties are politically mixed. The difference from 1976 to 2008 is striking: The number of light counties has fallen sharply. Roughly 25 percent more of the U.S. population now lives in a landslide county than did in the 1970s.

There is some truth to that, as liberals tend to love the center cities, and conservatives tend to move to the suburbs, and are most prevalent in rural areas.  I tend to credit population density as a contributing factor to political opinion.  If you are surrounded by lots and lots of people, you tend to have more appreciation for governmental activism.  If you live in the middle of nowhere, you don't see the need for any government involvement in your life, as long as your farm subsidy payment and your social security check keep coming, and as long as Medicare pays for your hip replacement.  Government shouldn't prevent industry from polluting, because when you are in the middle of nowhere, there isn't any industry.  That's my explanation for why the "Great American Desert" of the Great Plains is so red on the electoral maps, while the coasts are so blue.