San Diego is the eighth most populous city in the United States and second most populous in California (after Los Angeles). The City of San Diego recognizes 52 individual areas as Community Planning Areas. Within a given planning area there may be several distinct neighborhoods. Altogether the city contains more than 100 identified neighborhoods. 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 Marine Corps, and recent emergence as a healthcare and biotechnology development center.