There are 3,252 rail transit stations in the country. The Chicago region has 402. Walk half a mile from any one of those stations in any direction and you’re in its “transit zone.”

Transit zones are all over: from the loop, where they overlap, out to suburban Harvard and Harvey. What they have in common is potential. They can be convenient and cheap places to live, because being able to walk to a train can make a car less necessary. About a quarter of the region’s households live in transit zones, and their inhabitants are more nonwhite, a bit lower-income, and much less likely to drive to work than the average regional resident.

All this comes from a presentation (PDF) that the Center for Neighborhood Technology and the Chicago Rehab Network made on June 29. Their interest isn’t just academic. The way they see things going–and this is quite a change from the 1970s and 1980s–transit zones may gradually be priced out of most people’s reach. In what she calls the “Montrose Brownline TZ,” CNT research manager Carrie Makarewicz sees “apartments turning to condos, moderate single family homes being torn down and replaced with big high-end homes, etc.”

Transit zones are also the best chance for people to find affordable places to live–if you define “affordable” to include the cost of both housing and transportation, as the Center does. From a region-wide point of view, transit zones are also the obvious places to encourage walkable, high-density residential and commercial development.

But without some encouragement, gentrification could add another factor driving affordable housing out to the cornfields where cars become necessities, while transit zones fill up with condos and McMansions. If that’s fine with you, then don’t check out the full PowerPoint presentation, or John McCarron’s summary.