San Francisco, officially the City and County of San Francisco, is the 16th most populous city in the United States, and the fourth most populous in California, with 881,549 residents as of 2019. It covers an area of about 46.89 square miles (121.4 km2), mostly at the north end of the San Francisco Peninsula in the San Francisco Bay Area, making it the second most densely populated large U.S. city, and the fifth most densely populated U.S. county, behind only four of the five New York City boroughs. San Francisco is part of the 12th-largest metropolitan statistical area in the United States by population, with 4.7 million people, and the fourth-largest by economic output, with GDP of $549 billion in 2018. With San Jose, it forms the fifth most populous combined statistical area in the United States, with 9.67 million residents as of 2018. Colloquial nicknames for San Francisco include The City, SF, Frisco and San Fran.