San Diego (, Spanish: [san ˈdjeɣo]; Spanish for 'Saint Didacus') is a city in the U.S. state of California on the coast of the Pacific Ocean and immediately adjacent to the Mexican border. With a 2020 population of 1,386,932, San Diego is the eighth most populous city in the United States and second most populous in California (after Los Angeles). The city is the county 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 Marine Corps, and recent emergence as a healthcare and biotechnology development center. Historically home to the Kumeyaay people, San Diego is frequently referred to as the "Birthplace of California", as it was the first site visited and settled by Europeans on what is now the West Coast of the United States. Upon landing in San Diego Bay in 1542, Juan Rodríguez Cabrillo claimed the area for Spain, forming the basis for the settlement of Alta California 200 years later. The Presidio and Mission San Diego de Alcalá, founded in 1769, formed the first European settlement in what is now California. In 1821, San Diego became part of the newly declared Mexican Empire, which reformed as the First Mexican Republic two years later. California became part of the United States in 1848 following the MexicanAmerican War and was admitted to the union as a state in 1850. San Diego's main economic engines are military and defense-related activities, tourism, international trade, research, and manufacturing. The city is the economic center of the San DiegoTijuana conurbation, the second most populous transborder metropolitan area in the western hemisphere (after DetroitWindsor), home to an estimated 4,922,723 people as of 2012. The primary border crossing between San Diego and Tijuana, the San Ysidro Port of Entry, is the busiest international land border crossing in the world outside of Asia (fourth-busiest overall). The city's primary airport, San Diego International Airport, is the busiest single-runway airport in the world.

La Jolla ( lə HOY-ə, American Spanish: [la ˈxoʝa]) is a hilly, seaside neighborhood within the city of San Diego, California, occupying 7 miles (11 km) of curving coastline along the Pacific Ocean. The population reported in the 2010 census was 46,781.La Jolla is surrounded on three sides by ocean bluffs and beaches and is located 12 miles (19 km) north of Downtown San Diego and 45 miles (72 km) south of the Orange County line. The climate is mild, with an average daily temperature of 70.5 °F (21.4 °C).La Jolla is home to many educational institutions and a variety of businesses in the areas of lodging, dining, shopping, software, finance, real estate, bioengineering, medical practice and scientific research. The University of California, San Diego (UCSD), is located in La Jolla, as are the Salk Institute, Scripps Institution of Oceanography (part of UCSD), Scripps Research Institute, and the headquarters of National University (though its academic campuses are elsewhere).

Carlsbad is a coastal city in the North County region of San Diego County, California, United States. The city is 87 miles (140 km) south of downtown Los Angeles and 35 miles (56 km) north of downtown San Diego and is part of the San Diego-Chula Vista-Carlsbad, CA Metropolitan Statistical Area. Carlsbad is a popular tourist destination and notable home for many businesses in the golf industry. The city's estimated 2019 population was 115,382 and the median household is over $110,000.

Julian is a census-designated place (CDP) in San Diego County, California, in the United States. As of the 2010 census, the population was 1,502, down from 1,621 at the 2000 census. Julian is an official California Historical Landmark (No. 412). The Julian townsite and surrounding area is defined by the San Diego County Zoning Ordinance Section 5749 as the Julian Historic District. This designation requires that development adhere to certain guidelines that are administered by the Architectural Review Board of the Julian Historic District, which is appointed by the San Diego County Board of Supervisors.The town is known for its apple pie and its annual Julian Apple Days Festival, which began in 1949.