San Diego is a city in San Diego County, California, set along the Pacific coast just north of the U.S.–Mexico border. It is the county seat and one of the most populous cities in California, with roughly 1.4 million residents within the city and about 3.3 million across the county. The city wraps around San Diego Bay, a deep natural harbor that has anchored its identity from its founding through the present day. The bay has shaped San Diego's economy more than any other feature. San Diego is the principal West Coast home of the U.S. Navy's Pacific fleet, and military and defense-related activity remains one of the city's largest economic sectors alongside tourism, international trade, research, and manufacturing. The region has developed into a leading center for biotechnology and life sciences, clustered around institutions such as the University of California San Diego in La Jolla and San Diego State University farther east. This mix of naval installations, research campuses, and port commerce gives San Diego an economy distinct from many other coastal California cities. San Diego's landscape is defined by mesas, canyons, and a long stretch of Pacific shoreline, with distinct neighborhoods spread across the hills and valleys. Coastal communities such as La Jolla, Point Loma, Pacific Beach, and Ocean Beach frame the water, while older urban districts such as North Park, Hillcrest, and the Gaslamp Quarter form the city's cultural core. Inland valleys such as Mission Valley and newer communities to the north and east round out a housing stock that ranges from historic Craftsman and Spanish Colonial Revival homes to beach cottages, mid-century modern houses, and downtown high-rises. Residents are drawn to San Diego for its mild Mediterranean climate, its beaches and open space, and a lifestyle built around the outdoors. Balboa Park — the legacy of the 1915–16 Panama–California Exposition — anchors the cultural scene with its museums and the San Diego Zoo, while Mission Bay and the surrounding beaches provide year-round recreation. A network of freeways, the San Diego Trolley light-rail system, the Coaster commuter rail line into North County, and San Diego International Airport connect the city's dispersed neighborhoods and the wider region.