Any area with many residency programs (Phila, Chi, NYC, Miami, Cal, Det, etc) will be relatively saturated with those specialists. There are obviously a lot of local attendings supplying the training cases for the many residents in those cities, and many grad residents will stay in the area due to familiarity, good offers to join attending groups, etc.
Saturation is an important consideration, but if you have elite training and interpersonal skills, you shouldn't necessarily be intimidated by saturation. Ask yourself if your training gave you more services to offer patients than the next guy has, and also truly evaluate whether you are good at networking and making connections in the community (both the local medical professional community and the city in general). Keep in mind that saturated areas are also popular due to a huge patient base, so they also have the most growth potential.