San Francisco, officially City and County of San Francisco and colloquially known as SF, San Fran, Frisco, or The City, is the cultural, commercial, and financial center of Northern California. San Francisco is the 15th-most populous city in the United States, and the fourth-most populous in California, with 883,305 residents as of 2018. It covers an area of about 46.89 square miles (121.4 km), 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 the 12th-largest metropolitan statistical area in the United States by population, with 4.7 million people, and the 4th-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, the San Jose–San Francisco–Oakland, CA Combined Statistical Area (9.67 million residents in 2018).