The Weeds: the economic recovery has been concentrated in big cities. That’s a big problem.

Much of the criticism of our tepid economic recovery has focused on how it’s exacerbated wealth disparities between the very top and very bottom of the income distributions.

But there’s another important way in which the recovery from the Great Recession has widened preexisting disparities: by amplifying the difference in growth between big cities and small towns.

On the latest episode of The Weeds, Vox’s Matt Yglesias and Sarah Kliff discuss a new paper that shows that much of the growth in the recovery has really been concentrated in the most highly populated cities, while areas with lower population density have seen much slower growth. (Ezra Klein is off in California, learning that all of this might be a computer simulation anyway.)

Here’s Matt taking a look at some of the biggest factors that might be causing this shift:

We’ve especially seen growth in Brooklyn, Miami-Dade, San Francisco — a handful of big city places and not the vast yonder of the country. And that’s a big change. Some people looked at the math and said, “That’s not so bad,” but that’s missing the point.

You have the structural decline of physical goods retail — more and more, Amazon is how people are shopping. You’re not seeing physical stores vanish, but people aren’t building new ones at the rate they used to. It used to be taken for granted: If the economy is growing, we’ll need more stores. But the big city already has stores, and so it’s on the fringe where you’ll add new ones.

A related point is because we had such a crisis in the housing building industry people aren’t adding new homes at the rate they used to. That used to be a high-growth area — sprawl, exurbs — and we’ve seen very little homebuilding over the last few years.

And the last factor is the economy seems to have shifted to put more emphasis on the hottest big-city hubs. If you think about where there’s dynamism, it’s technology startups in big cities, and food startups and hospitalities in the big sectors have been growing a lot. … People want to find great places to eat and stay in nice hotels, and those are big city things.

Not only do you see this population shift, but the big cities aren’t growing that fast, either. Mostly, it’s been bad news overall in a decline of dynamism and growth. And that’s what’s really bad about it — if what had happened was small towns were doing poorly but big cities were having an insane boom, you might say, “Too bad for small towns.” But that’s not what’s happening.