[cadlin]

Homeless people congregate where there are services that are available to them. Predominantly, this means shelter and food. So homeless people will know when they can get food, from where, and this generally means places with high population density (it's much easier to walk from place to place in the city than in the suburbs!). In response to this, cities have passed a lot of NIMBY homeless shelter laws in their urban centers.

In Atlanta, there is a homeless shelter that is being closed down (it's currently in court) and the shelter can't relocate within the city because of laws on the size of homeless shelters. They were grandfathered in when the law was passed.

Source: I've spent a significant amount of time working with homeless shelters and on homeless policy.