The San Francisco Bay Area (referred to locally as the Bay Area) is a populous region surrounding the San Francisco and San Pablo estuaries in Northern California. The region encompasses the major cities and metropolitan areas of San Jose, San Francisco, and Oakland, along with smaller urban and rural areas.[3] The Bay Area's nine counties are Alameda, Contra Costa, Marin, Napa, San Francisco, San Mateo, Santa Clara, Solano, and Sonoma.[3][4] Home to approximately 7.65 million people,[1] the nine-county Bay Area contains many cities, towns, airports, and associated regional, state, and national parks, connected by a network of roads, highways, railroads, bridges, tunnels and commuter rail. The combined statistical area of the region is the second-largest in California (after the Greater Los Angeles area), the fifth-largest in the United States, and the 43rd-largest urban area in the world.