According to See California, the five largest cities in California as of 2015 are Los Angeles, San Diego, San Jose, San Francisco and Fresno. These are ranked according to population size.
Los Angeles is by far the largest city in California, with a population of more than 4 million. San Diego and San Jose each have more than a million people, and the population of San Francisco is nearing a million. Fresno has about half a million people.
The next five largest cities in California, according to See California, are Long Beach, Sacramento, Oakland, Santa Ana and Anaheim. Each of these cities has a population between 350,000 and 500,000, although Long Beach and Sacramento are very close to the half-million mark. Santa Ana is expected to grow significantly in the near future.
Another way to rank the largest cities in California is by land area. Using this method, Wikipedia lists California's top 10 as follows: Los Angeles, San Diego, California City, San Jose, Bakersfield, Fresno, Palmdale, Sacramento, Lancaster and Palm Springs. Lancaster has more actual land area than Palm Springs, but Palm Springs has more water area, thus making its total area greater than that of Lancaster.
By comparing the population size and land area of various cities, conclusions can be made regarding the population density. San Francisco, Long Beach, Oakland, Santa Ana and Anaheim are much more densely populated than California City, Bakersfield, Palmdale, Lancaster and Palm Springs.