San Diego is a coastal city in Southern California, situated near the US-Mexico border. As of 2021, San Diego County has an estimated population of 3,286,069, making it the fifth most populous county in the US. San Diego city, with a population of 1,386,932 in 2020, is the eighth largest city in the US. The city is famous for its year-round Mediterranean-style climate, deep-water harbor, numerous beaches and parks, proud history of serving the US Navy, and recent emergence as a biotechnology and healthcare hub. San Diego is California's second-largest city after Los Angeles.
The military and defense industries, tourism, foreign trade, research, and manufacturing are all critical to San Diego's economy. The city, with an estimated population of 4,922,723 in 2012, serves as the economic hub of the San Diego-Tijuana conurbation, the second-most populous transborder metropolitan area in the Western Hemisphere (after Detroit-Windsor).