Tuesday, April 21, 2009

Political geography

Jim Gimpel, guest blogging at the Monkey Cage, points out a fascinating ongoing project called the CommonCensus Map Project. So far, more than 50,000 people have been asked the question, "On the level of North America as a whole, what major city do you feel has the most cultural and economic influence on your area overall?" The answers have produced this map:You should really check out the version here that allows use of a magnifying glass. It's pretty fascinating. As Jim points out, it seems to overlap a lot with media markets. Thus people in western Nebraska and eastern Utah are more likely to identify with Denver because that's whose TV they watch.

This project helps answer a query that Lee Siegelman raised on Monkey Cage a few weeks ago. What's the best level to analyze the vote? Should we be looking at individual data? County returns? State returns? There's no obvious right answer here. Yes, individuals, not counties or states, are the ones that cast votes. But people are not islands. They often think as members of communities and evaluate political events in terms of their impact on their geographic area. There's some reason to think that counties are the relevant area to examine. People identify with their counties (much more than they do with their legislative districts, which shift frequently) as counties have relatively fixed borders, are host to many political contests, have set tax structures and public services that are often different from those of neighboring counties, etc. And yet some people may identify more with their county than others do. A resident of Compton probably has a very different conception of "L.A. County" than a resident of Woodland Hills does, even though they're in the same county.

Another nice take on American political geography can be found in the TPM Book Club's discussion of Andrew Gelman's book Red State, Blue State, Rich State, Poor State. The whole book is basically an examination of an ecological inference problem: wealthy states vote Democratic, while wealthy people vote Republican. Another way of stating the problem is, as one commenter notes, "mistaking the map for the territory."

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