Southern California is a geographic and cultural region that generally comprises California's southernmost 10 counties. Large urban areas include Greater Los Angeles and Greater San Diego.
Southern California is traditionally described as "eight counties", based on demographics and economic ties: Santa Barbara, Ventura, Los Angeles, San Bernardino, Riverside, Orange, San Diego, and Imperial. The heavily built-up urban area stretches along the coast from Ventura, through the Greater Los Angeles Area, the Inland Empire and down to San Diego. Southern California is a major economic center for the state of California and the United States.
Another definition based on historical political divisions involves 10 counties from San Luis Obispo County to the Mexican border and from the Pacific Ocean inland to Nevada and Arizona. The 8- and 10-county definitions are not used for the greater Southern California Megaregion, one of the 11 megaregions of the United States. The megaregion's area is more expansive, extending east into Las Vegas, Nevada, and south across the Mexican border into Tijuana.
Southern California's population encompasses eight metropolitan areas, or MSAs: the Los Angeles metropolitan area, consisting of Los Angeles and Orange counties; the Inland Empire, consisting of Riverside and San Bernardino counties; the San Diego metropolitan area; the Bakersfield metropolitan area; the Oxnard–Thousand Oaks–Ventura metropolitan area; the Santa Barbara metro area; the San Luis Obispo metropolitan area; and the El Centro area. Out of these, three are heavy populated areas: the Los Angeles area with over 12 million inhabitants, the Riverside-San Bernardino area with over 4 million inhabitants, and the San Diego area with over 3 million inhabitants. For CSA metropolitan 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. With over 22 million people, southern California contains roughly 60% of California's population.
To the east of southern California are the Colorado Desert and the Colorado River at the border with the state of Arizona and the Mojave Desert at the border with the state of Nevada. To the south lies the international border with Mexico, and to the west lies the Pacific Ocean.