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.
Xining, known as Qingtang City, Xiping County and Shanzhou in ancient times, is the capital of Qinghai Province, the political, economic, scientific and educational, cultural, transportation and communication center of Qinghai Province, and an important central city in the northwest region approved by the State Council. By 2019, the city had jurisdiction over five districts and two counties, with a total area of 7660 square kilometers, a built-up area of 129 square kilometers, a resident population of 2.3711 million, an urban population of 1.7098 million, and a urbanization rate of 72.1 percent. Xining is located in the eastern part of Qinghai Province, swimming in the river valley basin in the Huangshui River. It is the eastern gateway of the Qinghai-Tibet Plateau and the necessary place for the ancient "Silk Road" South Road and "Tangbo Ancient Road". It has been the northwest traffic road and military important place since ancient times. Known as the "key to the West Sea" and the throat of the sea, it is one of the high-altitude cities in the world and is also the State Council.