a new study from City Observatory, the number of young (25-34) college graduates living in city centers is up 37% since 2000, although the overall population of those areas has hardly changed. Dense, urban neighborhoods are the cool place to be. I am fascinated by this development. Is it just fashion? Is it because, as a real estate investor I know says, the affordable suburbs are just too far out now to be livable? (He expects that the next generation of slums will be suburbs an hour's drive from city centers.) Is it renewed environmentalism and a desire to bike to work and otherwise reduce carbon footprint a factor? Certainly there is a lot of evidence that young America's century-long love affair with cars has faded a little. Is it falling crime? Smaller families? A desire for lives that seem interesting rather than comfortable? All of those things?