The September 2011 issue of Scientific American is a great special issue on Smart Cities. Cities have challenges (pollution, crime, crowding, etc) but they also have a lot of advantages. With smart design, we can minimize the problems and maximize the benefits of density, including innovation, public transportation, smaller carbon footprints, vertical design, and more. The issue has a whole series of articles on various aspects of this idea. I recommend it if this is something you are even remotely interested in. It’s an excellent series.