San Francisco Bay Area as defined by

The San Francisco Bay Area, referred to locally as the Bay Area, is a geographically diverse metropolitan area that surrounds San Francisco Bay in northern California. Home to more than seven million people, it is composed of cities, towns, villages, military bases, airports, and associated regional, state, and national parks sprawled over nine counties and connected by a massive network of roads, highways, railroads, and commuter rail.
Because San Francisco was until recently the largest city in the region (it was surpassed by San Jose over 15 years ago in the 1990 census) and remains the traditional and cultural center, the region is identified with the city of San Francisco proper. However, San Francisco is neither dominant within the region in population (it is home to only 11% of the Bay Area's people) nor does it form a clear urban center to the Bay Area. Many residents now consider San Jose to be the dominant region of the Bay Area. This differs from more typical metropolitan areas that have a single urban center surrounded by dependent suburbs. The Bay Area is atypical in that its population is distributed across several regional urban and suburban centers. Due to the distributed and diverse nature of the region, it is referred to simply as the Bay Area (without reference to any specific city) by its residents; the fully qualified name is mostly used by outsiders and in formal and legal contexts.
Ultimately, the metropolitan area comprising the city of San Francisco together with Oakland and San Jose is the fifth-largest metropolitan area in the United States, after New York City, Los Angeles, Chicago and Washington, D.C.-Baltimore.

http://en.wikipedia.org/wiki/San_Francisco_Bay_Area