This nine- or ten-county area consists of cities of various size that lie more or less contiguously around the length of the bay. Three large cities dominate the area: San Francisco, San Jose, and Oakland. Because, unlike most other metropolitan areas in the United States, no single large city dominates the region, residents generally refer to the region generically as the Bay Area, without associating it with any one city. However, because San Francisco was historically the first major population center in the area, and because of its densely urbanized character in constrast to its neighbors, people in the region often refer to San Francisco as simply the City. Even San Jose natives, who live in the more populous city, will speak of "going to the City" when referring to a trip to San Francisco.
A more restrictive, informal definition includes only the urban portions of the previously defined area and also excludes Napa, Solano, and Sonoma counties, which are largely rural or suburban in character and have inland climates. High real-estate prices in this core of the Bay Area have driven many residents and businesses to move to outlying areas or to the Central Valley metropolitan areas of Sacramento, Stockton or Modesto, California area. As this trend continues, the definition of the Bay Area will likely expand, perhaps even including Yolo County as well.
Because the hills, mountains, and large bodies of water produce such vast geographic diversity within this region, the Bay Area offers a significant variety of microclimates. The areas near the Pacific Ocean are generally characterized by relatively small temperature variations during the year, with cool foggy summers and mild rainy winters. Inland areas, especially those separated from the ocean by hills or mountains, have hotter summers and colder overnight temperatures during the winter.
Skyline Boulevard stretches through the Santa Cruz Mountains, here near Palo Alto, California. During spring time the hills surrounding the Bay Area appear lush and green (image taken April 2004)
The population distribution of the Bay Area is generally subdivided into several smaller subregions.
The region north of the Golden Gate Bridge is known as the North Bay. This area consists of Marin County and extends northward into Napa and Sonoma counties. With some exceptions, this region is extremely affluent, and is generally the least urbanized part of the Bay Area, with many areas of undeveloped park and farm land. It is the only section of the Bay Area that is not served by a commuter rail transit service, though Sonoma-Marin service has entered the planning phase.
The eastern side of the bay, dominated by the city of Oakland but also including Berkeley, Richmond and several small cities, is known as the East Bay. The region, partly thanks to the Bay Area Rapid Transit (BART) rail service, has extended beyond the East Bay hills into suburban communities such as Walnut Creek, Concord and Antioch. The weather on the eastern side of the hills is markedly warmer in the summer as compared to San Francisco (which tends to maintain a rather moderate climate year-round).
The communities along the southern edge of the Bay are known as the South Bay. The South Bay covers roughly the same area as Silicon Valley, although some Peninsula and East Bay towns are sometimes included in the latter. It includes the cities of San Jose, Fremont, and the high-tech hub of Santa Clara, as well as many smaller communities.
The area between the South Bay and the city of San Francisco is known as the San Francisco Peninsula, locally just as The Peninsula. This area consists of a series of small cities and suburban communities along the Bay, as well as various towns along the Pacific coast.
San Francisco is generally placed in a category by itself, separated by water from the north and east, and by county line from its neighbor cities to the South (Locals refer to San Francisco as SF or The City. It is never referred to as San Fran or Frisco.) By extension, South San Francisco is often referred to as "South City," even though there are other towns between SSF and SF.
In some parts of the Bay Area rain is extremely rare during the summer months. As a result, the surrounding hills quickly become dry (image taken June 2004)
Bay Area Rapid Transit (BART) - A rapid transit electric train service that serves parts of the Bay Area, including San Francisco, Oakland, Berkeley, Fremont, and Walnut Creek. It also serves the San Francisco and Oakland airports.