"The truth is that New York, Chicago and most of the older American cities had their greatest growth before there was anything resembling real public planning; the most basic American land planning tool, zoning, did not come into widespread use until the 1920s.
L.A... was one of the country's zoning pioneers. It has had most of its growth since the 1920s, during a period when planning was already important, and particularly since World War II, when California cities have been subject to more planning than cities virtually anywhere else in the country.
...The result is that today the Los Angeles urbanized area, as reported by the U.S. Census Bureau, has just over 7,000 people per square mile â€" by a fair margin the densest in the United States.
Many people think that this must be a statistical trick because no part of the L.A. region could possibly be as dense as Manhattan or central Chicago. But there is no trick. Los Angeles has always had relatively small lot sizes, very little abandonment and, because of the difficulty in obtaining water, almost none of the really low-density suburban and exurban development that extends for dozens of miles in all directions outside older cities in the northern and eastern United States."