The Valley

San Francisco, officially the City and County of San Francisco, is the financial, cultural, and transportation center of the San Francisco Bay Area. The only consolidated city-county in California, it encompasses a land area of 46.9 square miles (121 km2) on the northern end of the San Francisco Peninsula, giving it a density of 17,179 people per square mile (6,632/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.

During the dot-com boom of the late 1990s, startup companies invigorated the economy. Large numbers of entrepreneurs and computer application developers moved into the city, followed by marketing and sales professionals, changing the social landscape as once-poorer neighborhoods became gentrified. When the bubble burst in 2001, many of these companies folded, and their employees left, although high technology and entrepreneurship continue to be mainstays of the San Francisco economy.

San Francisco's economy has increasingly become tied to that of its Bay Area neighbor San Jose and Silicon Valley to its south, sharing the need for highly educated workers with specialized skills. Due to such links with Silicon Valley, San Francisco became an epicenter of the Dot-Com bubble of the 1990s–2000s, and the subsequent Web 2.0 boom of the late 2000s. Many popular and prominent Dot-Com companies and "start-ups" such as Craigslist.org, Twitter, and the Wikimedia Foundation among others have established their head offices in San Francisco.

Today, San Francisco is a popular international tourist destination, renowned for its chilly summer fog, steep rolling hills, eclectic mix of Victorian and modern architecture, and its famous landmarks, including the Golden Gate Bridge, cable cars, and Chinatown. The city is also a principal banking and finance center, and the home to more than 30 international financial institutions, helping to make San Francisco rank eighteenth in the world's top producing cities, ninth in the United States, and thirteenth place in the top twenty global financial centers.