This is also a pretty inaccurate way of looking at it. Sure it may be the shortest distance from the geographical center of the city, but that doesn't mean all of these other cities neighborhoods aren't densely populated with sprawl. Take San Diego for example, they cannot expand that airport because the highrise sprawl basically goes right up next to it. Same with HNL and SJC. The list goes on... there are actually very few on that list that if you actually go in and look at their situations individually you'll find they are removed from dense areas (SMF, BWI, AUS, etc.)