One area of urban planning that I have both read a lot about, in the sense that it exists, but have not read anything about, in the sense of what a planner can/should do about it, is segregation.
h/t to Ms. AK from Seattle for the link to these illuminating population maps. Just goes to show how far a good visual can go. I've posted three, but a few more are here.
Red/pinkish dots = white people, blue dots = black, green dots = asian (presumably east asian, judging by the Chinatown clusters, unknown how much of Asia is included though), and yellow = hispanic/latino.
San Francisco - lots of white people in north and central SF. Interesting integration in what looks to be either downtown Oakland or Berkeley, can't quite tell. It's one of the few places on any map where all colors can be seen mixed together.
Detroit - the 8 mile road is like the Berlin Wall. Wow. Inner city is black, outer ring, white.
New York City - the famous neighborhoods. Little thises and thatses, and boy are they concentrated. Notable that Central Park and Prospect Park, the two best known (and used) parks, are pretty much surrounded by white people. Assuming I've noted the correct location for Prospect. I guess that shouldn't really come as much of a surprise.
These maps = me looking forward to learning GIS.