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The growth of Los Angeles is a 20th century phenomenon, according to U.S. Census data. In 1910 it is not even one of the top ten most populous cities in the U.S.A. In 1920, it is the tenth most populous city. In 1930, it has jumped to being the fifth largest city, and remains at fifth in 1940. In 1950 it is America's fourth largest city. In 1960, 1970 and 1980 it stands as the third largest city. Only in 1990 does it come in second place to NYC, where it has remained until the present day. It is no accident that these dates correspond with the rapid growth of Hollywood and the entertainment and mass communication industries in the 20th century. Los Angeles is a particularly good location for outdoor filming, though: it seldom rains (only a few days a year) and by and large the climate is warm, sunny, and pleasant (as Angelenos never stop reminding New Yorkers). It has the benefit of being essentially a desert climate, while still situated on the Pacific ocean which softens the harsher effects of a desert clime: this means that the air remains largely cloudless (although not smogless) while temperatures become chilly at night. Nonetheless, the susceptibility of Los Angeles to wildfires, mudslides and earthquakes indicates that there are some tradeoffs for having nice weather all the time.

But there is more to California than Hollywood: San Diego, the second most populous area in the state, has a large military and defense presence. San Jose and San Francisco are third and fourth in terms of size. San Francisco was a major shipping port throughout the 19th century, and the two cities remain the urban centers of the "Silicon Valley" high tech industries. The northern part of California is different in many ways from Los Angeles, however. The climate becomes more like the rainy misty Pacific northwest, and agriculture and timber become more important to the economy. Northern California is the world's largest producer of almonds; Southern California produces nuts of an altogether different sort.

Los Angeles and New York are similar in a way that is familiar to metropolitan areas that depended upon old methods of transportation: they are both situated on the coasts, and their locations afford natural harbors to some degree. NYC is better for shipping, due to the confluence of rivers flowing to the Atlantic, and the presence of large barrier islands protecting its harbors. But in both cases, urban expansion runs up against natural barriers: in the case of NYC, the city is built on islands, so expansion is limited by space. In California, expansion is limited by surrounding mountains, and also by the relative scarcity of water.