Since my last post, I was reminded of the existence of this, from Radical Cartography. One point Bill Rankin makes there, which is really important, is that the “donut model” of economic geography, with concentric circles of high- and low-income areas, is really not the American standard. More common is the “wedge model,” with a “favored quarter” radiating out from the city center like an especially privileged slice of pizza.

For example (in Rankin’s maps, pink = rich and blue = poor):

If you take another look at my maps for Chicago…

…you might reasonably ask: how sure are you that the growth of a high-income zone in the central city is following the donut model, versus the wedge model? After all, it seems to be growing mostly towards the already super-wealthy northern suburbs. Maybe the endgame is a wedge, after all.

To which I would reply: yes, I think there’s something to that. But what matters, I think, is what’s at the center. Going back to the rent gap theory, a building’s potential rents will only be high if it’s close to jobs or amenities that make the area valuable. In all of the extreme wedge examples above, the downtowns don’t really serve quite the same central economic or cultural role for their respective metropolitan areas as does downtown Chicago, and so areas adjacent to them – say, the southern end of downtown Atlanta, or the areas to the north of downtown St. Louis – aren’t especially close to a major job or amenity center. Instead, those centers are further out in the suburbs, and high rents revolve around them, following major transportation corridors.

In other words, northern Bronzeville’s position, I’m guessing, really isn’t anything like whatever neighborhoods are a mile or three east of downtown Houston: it’s actually in close proximity to the region’s largest amenity hub, and they aren’t.

Now, what gives the wedge model a bit of weight in Chicagoland is that the Loop isn’t the only major employment center. In fact, even if you know nothing about the Chicago area, you could easily pick out the other employment centers just by looking at the map: they’re in the northern suburbs and along a corridor running along I-88 in second- and third-ring suburbs southwest of the Loop. They are, not coincidentally, close to the two largest other major high-income areas. (Though the high-income areas near I-88 continue to move away from where the actual jobs are, which is something that should maybe trouble people with a vested interest in keeping those jobs there.)

Anyway, the point is that things are complicated, and basically every major metropolitan region in the world is polycentric, which does weird things to potential rents, and thus the prospects of disinvestment and reinvestment. You don’t even have to go outside the city to see that: though it’s much less dramatic, Hyde Park – the little patch of white along the south lakefront – has seen a very small ripple of reinvestment expand from its major employment center, the University of Chicago. The problem there, of course, is that Hyde Park is surrounded entirely by black neighborhoods (and South Kenwood, a mixed neighborhood, beyond which is North Kenwood, and almost entirely black neighborhood), which, as we discussed last time, makes the reinvestment stage difficult.