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.
Tongling, a prefecture-level city in Anhui Province, is located in the south-central part of Anhui Province and the lower reaches of the Yangtze River, with Hefei to the north, Chizhou to the south, Wuhu to the east and Anqing to the west, with a total area of 3008 square kilometers. Tongling gets its name from copper and flourishes with copper. it is known as "the ancient copper capital of China and the contemporary copper base". The history of copper mining began in the Shang and Zhou dynasties, flourished in the Han and Tang dynasties, and lasted for more than 3500 years. The first furnace of copper water and the first copper ingot in New China came from Tongling. The first copper industrial base was built in Tongling, and the first copper stock was issued in Tongling. In 2018, Tongling had jurisdiction over three municipal districts and one county, with a resident population of 1.629 million, achieving a GDP of 122.24 billion yuan, of which