Population Density, Water, and Politics

There's a strong correlation between population density and voting for Democrats. I have also noticed a correlation between proximity to water and voting for Democrats. The “blue” counties tend to concentrate on the sea coasts and Great Lakes, and along the Mississippi and Rio Grande rivers. (Cf. John Tierney in The New York Times.)

Water may be a more important explanation than density. Low-density counties along the Mississippi often went Democratic. In North Carolina, the more-urbanized inland voted Republican and the more-rural seacoast voted Democratic.