A Bloomberg story notes that declines in home prices have hardly been uniform. Thanks to the rising cost of gasoline, things are much worse in far-flung exurbs than they are in closer-in territories. This is one of several factors that could lead, as Christopher Leinberger predicted, to the far-out suburb being the next slum. The trouble of course is that under a scenario like that, high energy costs will disproportionately bite the poor to an even greater extent than they do today.

The solution, as Ryan Avent says, is to build denser communities. We ought to build more transit infrastructure, of course, but it's cheaper to use what we already have more intensively. And, of course, it's more practical to build new infrastructure if there's a reasonable expectation that it will serve intensive development. Beyond that, density also serves to make walking and biking more practical for more trips. And best of all, getting denser could be accomplished mostly through growth-enhancing relaxation of regulatory burdens.

In that spirit, it's worth noticing some stuff about the math of density. Back when I was in college, I never thought of Cambridge as a particularly high-density place -- it's certainly not dominated by skyscrapers or large apartment towers or anything of the sort. But it turns out to have over 15,700 residents per square mile. If DC were as dense as Cambridge, we'd have about a million people living here. And if Fairfax County were as dense as Cambridge, it would fit six million people. And of course if the supply of housing in central cities and nearby suburbs were radically higher, then it would be much easier for people to afford to live in them. Instead, restrictions on the supply of conveniently located housing lead to high prices and the "drive until you qualify" phenomenon that's currently leaving many Americans in deep trouble as they try to pay for fuel.

We want to hear what you think about this article. Submit a letter to the editor or write to letters@theatlantic.com.