L.A.'s population density: 12,114 people per square mile

That might seem awfully tight considering that metro areas with fewer than 250,000 people have a density of closer to 1,600. But it's positively spacious compared with the NY metro area, which has a density of 31,251 people per square mile, according to the Census Bureau. That's by far the highest level in the country. So is density a good thing? Does it lead to greater creativity and shorter commute times and thriving economies and a better understanding of your fellow man? City Hall's unequivocal view is that density rocks. That's why you see so much development of mixed-use projects near mass transit stops. That's why the city is tossing out incentives to most any developer who has a pulse and wants to build downtown and in Hollywood. Everyone chooses to believe that urban density is a good thing, but the evidence remains flimsy. From the Atlantic's Richard Florida:

Density has long been seen as a key factor in the ability of cities to innovate and grow, but exactly how it does so remains an open question. [A study by Jordan Rappaport of the Kansas City Fed] suggests that there is not a one-to-one relationship between density and productivity, noting that the "productivity required to sustain above-average population densities considerably exceeds estimates of the increase in productivity caused by such high density." Silicon Valley remains tremendously innovative at medium levels of density. The world's densest cities in Asia and elsewhere can take the form of skyscraper districts which limit interaction and function as kind of vertical sprawl. At the same time, more and more start-ups and innovative high-tech firms are choosing locations in the urban districts of New York, London, San Francisco, Boston, and other cities, as opposed to the traditional industrial and office parks of suburban nerdistans.