> DC and Baltimore are vastly different in culture, recreational activities, industries, demographics, etc. People don't live downtown in one and work in the ot

> DC and Baltimore are vastly different in culture, recreational activities, industries, demographics, etc. People don't live downtown in one and work in the other. The commute would kill you. Average income in DC is nearly double what it is in Baltimore. Culture, recreational activities, demographics, etc. vary quite a bit in other "twin city" type situations as well. Dallas and Fort Worth are about as culturally different as you can get at that distance, and of course people don't live downtown in one and work in the other - people are making a very specific choice with very specific tradeoffs when it comes to living in a downtown area in general, and those don't make sense if you're not explicitly spending most of your time in that area. Income is about the only thing that doesn't hold true in the Texas and Minnesota examples listed elsewhere in the comments, and DC has some conditions fairly specific to it that cause that.