San Diego is the second largest city in California and the seventh largest in the United States, and has an excellent natural harbor. It is an important port of entry; a shipping and receiving point for S California, Arizona, New Mexico, and Mexico's Baja California; and headquarters for the 11th U.S. naval district. San Diego has large aerospace, electronic, and shipbuilding industries, and is an important center for the wireless communications industry, biomedical research, biotechnology industries, and oceanography. It is also a distribution and processing point for a highly productive agricultural area. Other manufactures include industrial instruments and machinery, computer hardware and software, apparel, and processed foods. Tourism is an important element in the economy; the city has a delightful climate, miles of beaches, historic attractions, and a proximity to Mexico.