San Diego (/ˌsæn diˈeɪɡoʊ/ SAN dee-AY-goh, Spanish: [san ˈdjeɣo]; Spanish for 'Saint Didacus') is a city on the Pacific Ocean coast of Southern California located immediately adjacent to the Mexico–United States border. With a 2020 population of 1,386,932, it is the eighth most populous city in the United States and the seat of San Diego County, the fifth most populous county in the United States, with 3,338,330 estimated residents as of 2019. The city is known for its mild year-round climate, natural deep-water harbor, extensive beaches and parks, long association with the United States Navy, and recent emergence as a healthcare and biotechnology development center. San Diego is the second largest city in the state of California, after Los Angeles.
Longnan, the prefecture-level administrative district (city) under the jurisdiction of Gansu Province, is located at the southeast end of Gansu Province, bordering Shaanxi Province to the east, Nantong Sichuan Province, and the three provinces of Shaanxi, Gansu and Sichuan. It is a strategic passage connecting Lanbai, Chengdu and Chongqing, and Guantian three major economic zones. Northwest-southwest important transportation hub connection, known as "Qinlong lock key, Ba Shu throat". It has jurisdiction over Wudu District, Kang County, Wen County, Cheng County, Huizhou County, Liangdang County, Xihe County, Li County and Dangchang County, covering an area of 27900 square kilometers and a total population of 2.8816 million (2018). Longnan is located in the Qinba Mountains, the Loess Plateau and the Qinghai-Tibet Plateau.