This note by Nate inspired me to check the vote swings by county population. I don’t have the urban/suburban/rural status of counties in an easily grabbable form (maybe Boris has these and can send to me) and so as something quick I plotted vote swing vs. county population. Actually, I don’t have county population right here either and so I used total number of votes in the county in 2004. Many of the large-population counties are urban (such as Los Angeles, the largest); others are major suburban counties. Anyway, here’s what we see:

The blue line is the lowess curve fit to the data. There’s a lot of variation–county size is not such a good predictor of swing–but there is indeed a pattern of bigger Obama swings in larger counties. (The counties are already ordered by size so there’s no need to use larger circles to indicate larger counties as I did in the plots of county income posted earlier.)

To understand this better, let’s break up the data by region of the country. Also, since we’re at it, let’s look at swings in the past couple of elections as well.

Here are the swings broken up by region of the country for the past few elections. The left column shows 1996/2000, the middle column shows 2000/2004, and the right column shows 2004/2008.

What do we see?
1. The large-county/small-county differential in Obama’s gains was particularly strong in the south and did not occur at all in the northeast. For example, Obama won 84% of the two-party vote in Philadelphia–but Kerry got 80% there four years ago. This 4% swing was about the same as Obama’s swing nationally. Part of the issue here is that Obama had almost no room for improvement in these places.

2. The pattern of Democrats improving more in large-population counties is not unique to 2008. Gore did (relatively) well in big counties in all regions in 2000.