The population within the city limits of Los Angeles exceeded 4,000,000 for the first time in 2007, up 1.2% from 2006.That reminds me of a novel question: What urban area in the U.S. has the highest population density per floor? For example, the wealthy Upper East Side in Manhattan has a very high population density per acre of ground because it`s covered with high rise apartment buildings. Yet, the density per acre divided by the average number of floors on the Upper East Side is not all that high because the amount of floor space is large and households are small.So, where is the lowest number of square feet of residential space per resident found?One contender for that dubious title would have to be the Hollywood neighborhood in LA. Hollywood is mostly low rise, but the side streets are absolutely crammed with pedestrians. At the corner of two side streets in a residential area of mostly one story homes, you`ll see a guy with a card table on the sidewalk selling oranges.I imagine Chinatown in lower Manhattan has even fewer square feet per resident—I gather hotbunk dormitories, where the same bed is rented by three different sleepers working on different shifts are not uncommon there — but Hollywood is still way up there.I would bet that more than a few people who thought it was a good idea to immigrate to Hollywood find it`s not quite as glamorous as they imagined.