Southern California (colloquially and locally known as SoCal) is a geographic and cultural region that generally comprises California’s southernmost counties, and is the second most populous urban agglomeration in the United States. The region is traditionally described as eight counties, based on demographics and economic ties: Imperial, Los Angeles, Orange, Riverside, San Bernardino, San Diego, Santa Barbara, and Ventura. The more extensive 10-county definition, which includes Kern and San Luis Obispo counties, is also used and is based on historical political divisions.
The 8-county and 10-county definitions are not used for the greater Southern California Megaregion, one of the 11 megaregions of the United States. The megaregion is more expansive, extending east into Las Vegas, Nevada and south across the Mexican border into Tijuana.
Southern California includes the heavily built-up urban area which stretches along the Pacific coast from Ventura through the Greater Los Angeles area and the Inland Empire, and down to Greater San Diego. Southern California’s population encompasses eight metropolitan areas: the Los Angeles metropolitan area (Los Angeles and Orange counties), the Inland Empire (Riverside and San Bernardino counties), the Palm Springs and Indiometropolitan area (Coachella Valley), the San Diego metropolitan area, the Oxnard–Thousand Oaks–Ventura metropolitan area, the Santa Barbara metropolitan area, the San Luis Obispo metropolitan area, and the El Centroarea. The Los Angeles area has over 12 million inhabitants, while the Riverside-San Bernardino area has over 4 million inhabitants and the San Diego area has over 3 million inhabitants. For Combined Statistical Area (CSA) purposes, the five counties of Los Angeles, Orange, Riverside, San Bernardino, and Ventura, are all combined to make up the Greater Los Angeles area with over 17.5 million people, the second-most populous U.S. combined statistical area, after the New York metropolitan area. With over 22 million people, southern California contains roughly 60 percent of California’s population.
The Colorado Desert and the Colorado River are located on southern California’s eastern border with Arizona, and the Mojave Desert is located north on California’s Nevada border. Southern California’s southern border is part of the Mexico–United States border.