San Francisco, officially the City and County of San Francisco, is the financial, cultural, and transportation center of the San Francisco Bay Area, a region of 7.5 million people which includes San Jose and Oakland. The only consolidated city-county in California, it encompasses a land area of about 46.9 square miles (121 km2) on the northern end of the San Francisco Peninsula, giving it a density of about 17,179 people per square mile (6,632 people per km2). It is the most densely settled large city (population greater than 200,000) in the state of California and the second-most densely populated large city in the United States after New York City. San Francisco is the fourth most populous city in California and the 13th most populous city in the United States, with a population of 805,235 as of the 2010 Census. The San Francisco-Oakland-Fremont metropolitan area has a population of 4,335,391.

San Diego, named after Saint Didacus, is the eighth-largest city in the United States and second-largest city in California after Los Angeles, with a population of 1,306,300 (Jul 2009) within its administrative limits on a land area of 372.1 square miles (963.7 km2). The city is located on the coast of the Pacific Ocean in Southern California. The urban area of San Diego extends beyond the administrative city limits with a population of 2,880,000. San Diego is also the county seat of San Diego County, the 5th largest county, by population, in the United States.