I currently live in the place that the plot of this movie centers around. The post war San Fernando Valley(yes, that Valley where the Valley Girl phenomenon originated) that exploded with development after WWII. Before the war the valley was largely orange and walnut groves and before the big boom, the government built many Defense plants here to build and develop most of it's planes. To accommodate the many employees of these plants, housing developers moved in and there were many power grabs of which these 2 movies revolve around. After the infusion of the water that was brought in via the Mullholland Dam Project (part of the plot of Chinatown) the population of the Valley grew in leaps and bounds! What was a pleasant drive in the "country" as Los Angeleans referred to the SFV as, before the late 40's, became the largest housing boom the country has ever seen before or since! Currently there are at least 3 million people living here(many undocumented immigrants live here uncounted). Anyone who owned land became wealthy including the late Bob Hope who owned vast amounts of Valley acreage! Many of the farmers from back then ( like Van Owen and Van nuys) sold thier land and became very rich. I think that the John Huston character from Chinatown was based on one of the Van characters. They even named major avenues in the Valley after Van Nuys and Van Owen. I think that the actual filming of the movie was shot north of the San Fernando Valley because it is all developed now. I am too young to remember the era of this movie but i can appreciate since I live in LA and can see many of the buildings seen in the Hollywood and downtown scenes that still stand and look just like they did then! I loved this movie for the many ways it captured the era. One scene where Jake is driving you can hear on the radio the serial "The Whistler", which is still played among others on the Oldtime Radio Hour, on a local AM station 1070. True, this town isn't as old or historical as a Boston or New York or Philadelphia, but it has had it's moments and it's moods are reflected well in this movie. If you don't at first understand the plot, maybe it isn't as complex as it may seem. It's about a part of our country that exploded with growth and opportunities perhaps like none other and of course there will be visionary people trying to capitalize on that and make a fortune.
