Yep. When visiting SF, I tried to walk a lot to see the city change. Going into different neighborhoods felt more like stepping into completely different cities. I'd hear X neighborhood was full of Y, and it was exactly that. Perhaps it blends more once you live there, but I was really struck by the cultural divisions.
Well after seeing those "postcards", cartoonish is becoming clearer. As a child in SF, I remember each neighborhood changing ONLY as you got to the center of each hood. There used to not be any strong demarcation lines, if that makes sense. Perhaps that's grown out of the overpopulation?