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.
Ya'an, a prefecture-level city of Sichuan Province, is located at the western edge of Sichuan Basin and the eastern foot of Qionglai Mountain, with Chengdu, Ganzi to the east, Liangshan to the south and Aba to the north, 120km away from Chengdu; it belongs to the mountainous area on the western edge of Sichuan Basin, spanning the Sichuan Basin and the Qinghai-Tibet Plateau; the climate type is subtropical monsoon humid climate; the total area of the city is 15046 square kilometers, under the jurisdiction of 2 districts and 6 counties; the total population in 2017 is 1.5378 million. Ya'an is located at the intersection of Sichuan-Tibet and Sichuan-Yunnan Highway, 120 kilometers away from Chengdu. It is the transition zone between Sichuan Basin and Qinghai-Tibet Plateau, the transition zone between Han culture and national culture, and the transition zone between modern central city and primitive natural ecological area. it was the gateway and necessary road of the ancient southern Silk Road and was once the capital of Xikang Province. It is the history and culture of Sichuan Province.