San Francisco, officially the City and County of San Francisco, is a commercial and cultural center in Northern California. The city proper is the 17th most populous in the United States, and the fourth most populous in California, with 815,201 residents as of 2021. It covers a land area of 46.9 square miles, at the end of the San Francisco Peninsula, making it the second most densely populated large U.S. city after New York City, and the fifth most densely populated U.S. county, behind only four of the five New York City boroughs. Among the 331 U.S. cities proper with more than 100,000 residents, San Francisco was ranked first by per capita income and fifth by aggregate income as of 2019. Colloquial nicknames for San Francisco include SF, San Fran, The City, Frisco, and Baghdad by the Bay.