How the Density of Your County Affects How You Vote

Political scientists and party activists continue to sift through the demographic tea leaves left behind by the last election—the Democrats' white South problem, the Republicans' larger race problem, the growing generational divide. But the most striking gap between the parties is not the race or age or even income of voters. It's how close they live to each other.

The map below follows up on the insights of Dave Troy, who finds a decisive break between Democratic and Republican support at a population density of about 800 persons/per square mile. In less-densely populated counties, about two-thirds voted for Romney; in more-densely populated counties, about two-thirds voted for Obama. The distinction here is not between suburban conservatism and skyscraper liberalism: even most small cities and suburbs have thousands of persons per square mile (Cedar Rapids, Iowa, for example, has a population density of about 2400/sq mile).