The San Francisco Bay Area, commonly known as the Bay Area, or the Bay, is a metropolitan region that surrounds the San Francisco and San Pablo bays in Northern California.

It encompasses large cities such as San Francisco, Oakland, and San Jose, along with smaller urban and rural areas. Overall, the Bay Area consists of nine counties, 101 cities, and 7,000 square miles. The nine counties are Alameda, Contra Costa, Marin, Napa, San Francisco, San Mateo, Santa Clara, Solano, and Sonoma.

The Bay Area encompasses the metropolitan areas of San Francisco (12th largest in the country) and San Jose (31st largest in the country), as well as four other smaller, surrounding metropolitan areas. When defined as a Combined Statistical Area, the Bay Area is the sixth largest in the country, including over 7.2 million people. The Bay Area hosts many cities, towns, military bases, airports, and associated regional, state, and national parks, connected by a massive network of roads, highways, railroads, bridges, tunnels and commuter rail. The combined urban area of San Francisco and San Jose is the 49th largest urban area in the world.

San Francisco is the financial center of the Bay Area (and has the second highest density rate in the nation after New York City), while San Jose is the center of Silicon Valley and the most populous city. The Bay Area is renowned for its natural beauty, liberal politics, affluence, diversity, and new age reputation.

The Bay Area is home to more than seven million people. The San Francisco Bay Area is one of the wealthiest regions in the United States. According to the United States Census Bureau, of the 280 defined metropolitan areas, the San Francisco Bay Area has the highest median household income in the nation with $62,024 in the year 2000. The Census Bureau also released data in August 2006 citing San Jose as having the second highest median household income among large cities. Among medium-sized cities, Pleasanton has the highest household income in the country, and Livermore the third highest. The popularity of the region, owing both to its mild weather and its cultural and economic diversity, combined with limited buildable areas, has led to high housing costs, especially for ownership and for commercial property leases.

Courtesy of www.wikipedia.org