So, yesterday Obama said something about the age of sprawl being over. This got the urbanist community all aflutter. I think it’s nice to have things like that said, but I’ve also heard Obama say enough things like that that it’s no longer personally uplifting. I’m waiting, at this point, for the meat.

But the declaration leads the Wire to ask just what counts as sprawl. I think sprawl is used to capture to separate concepts, which serve to be treated separately. One is compactness; the other, dispersion. Or to put it another way, one is neighborhood density; the other, regional density.

You can have a metropolitan area contained in a relatively small geographic space which is also sprawling — a good example would be Los Angeles. And you can also have a highly dispersed metropolitan area with compact neighborhoods. This was the dominant development pattern in the age of the railway, when small, walkable towns grew up around rail stations. And you can have other combinations as well.

We should be less concerned about regional density, which is heavily influenced by economic and geographic variables. Economic areas in the northeast are quite thick with population centers, while the Midwest is more dispersed, and the Mountain west is highly dispersed. There’s only so much policymakers can or should do to influence these outcomes. (Though as I have mentioned often at this site, we can reduce economic distances between remote places with better infrastructure, which would be productivity improving).

But neighborhood density is highly determined by policy variables, and is properly considered “sprawl.” I don’t think there’s any special trick to addressing compactness. If you price roads properly, neighborhoods will be more compact. If you increase gas taxes, they’ll be more compact. If you remove regulations that prevent compact development, they’ll be more compact. And if you tailor infrastructure toward compact building, they’ll be more compact. Some of these variables are more important than others. Transit construction alone doesn’t generate compactness if land-use controls are awry and negative externalities are unpriced.

But there’s no reason to look at sprawl as an uncontrollable or unfathomable occurence. We get it because we planned for it. If we tolled congested highways and increased the gas tax by $1 per gallon, then in a decade’s time, new neighborhoods would be much more compact.