With an estimated population of 1,406,630 as of July 1, 2016, San Diego is the eighth-largest city in the United States and second-largest in California. It is part of the San Diego–Tijuana conurbation, the second-largest transborder agglomeration between the US and a bordering country after Detroit–Windsor, with a population of 4,922,723 people.[12] San Diego has been called "the birthplace of California".[13] It is known for its mild year-round climate, natural deep-water harbor, extensive beaches, long association with the United States Navy, and recent emergence as a healthcare and biotechnology development center.