LudditeOne: It does seem to be more conventional to note U.S. states’ most populous cities in lead for U.S. states’ second cities; this should be an improvement

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”’San Diego”’ ({{IPAc-en|ˌ|s|æ|n|_|d|i|ˈ|eɪ|ɡ|oʊ}} {{respell|SAN|_|dee|AY|goh}}, {{IPA-es|san ˈdjeɣo|lang}}; {{langnf||Spanish|[[Didacus of Alcalá|Saint Didacus]]}}) is the [[List of municipalities in California|second largest city]] in the [[U.S. state]] of [[California]], located on the coast of the [[Pacific Ocean]] and immediately adjacent to the [[Mexico–United States border]]. With a 2020 population of 1,386,932,<ref name=”QuickFacts”>{{cite web |title=QuickFacts: San Diego city, California |url=https://www.census.gov/quickfacts/fact/table/sandiegocitycalifornia/POP010220 |publisher=United States Census Bureau |access-date=20 August 2021}}</ref> it is also the [[List of United States cities by population|eighth most populous city in the United States]] and the [[county seat|seat]] of [[San Diego County]], the [[List of the most populous counties in the United States|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 Armed Forces|U.S. armed forces]], and recent emergence as a healthcare and [[biotechnology]] development center.

”’San Diego”’ ({{IPAc-en|ˌ|s|æ|n|_|d|i|ˈ|eɪ|ɡ|oʊ}} {{respell|SAN|_|dee|AY|goh}}, {{IPA-es|san ˈdjeɣo|lang}}; {{langnf||Spanish|[[Didacus of Alcalá|Saint Didacus]]}}) is a city on the [[Pacific Ocean]] coast of [[Southern California]] located immediately adjacent to the [[Mexico–United States border]]. With a 2020 population of 1,386,932,<ref name=”QuickFacts”>{{cite web |title=QuickFacts: San Diego city, California |url=https://www.census.gov/quickfacts/fact/table/sandiegocitycalifornia/POP010220 |publisher=United States Census Bureau |access-date=20 August 2021}}</ref> it is also the [[List of United States cities by population|eighth most populous city in the United States]] and the [[county seat|seat]] of [[San Diego County]], the [[List of the most populous counties in the United States|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 Armed Forces|U.S. armed forces]], and recent emergence as a healthcare and [[biotechnology]] development center. San Diego is the [[List of municipalities in California|second largest city]] in the [[U.S. state|state]] of [[California]] after [[Los Angeles]].

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|U.S. west coast]].<ref>{{cite book|last=McGrew|first=Clarence Alan|url=https://archive.org/details/citysandiegoand00socigoog|title=City of San Diego and San Diego County: the birthplace of California|publisher=American Historical Society|year=1922|access-date=July 23, 2011}}</ref> 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 of San Diego|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 [[First Mexican Empire|Mexican Empire]], which reformed as the [[First Mexican Republic]] two years later. California became part of the U.S. in 1848 following the [[Mexican–American War]] and was admitted to the union as a state in 1850.

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|U.S. west coast]].<ref>{{cite book|last=McGrew|first=Clarence Alan|url=https://archive.org/details/citysandiegoand00socigoog|title=City of San Diego and San Diego County: the birthplace of California|publisher=American Historical Society|year=1922|access-date=July 23, 2011}}</ref> 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 of San Diego|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 [[First Mexican Empire|Mexican Empire]], which reformed as the [[First Mexican Republic]] two years later. California became part of the U.S. in 1848 following the [[Mexican–American 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 Diego–Tijuana]] [[conurbation]], the second most populous [[transborder agglomeration|transborder metropolitan area]] in the [[Western Hemisphere]] (after [[Detroit–Windsor]]), home to an estimated 4,922,723 people as of 2012.<ref>{{cite book|url=http://world-gazetteer.com/wg.php?x=&men=gcis&lng=en&dat=32&geo=-2&srt=pnan&col=aohdq&va=&pt=a|title=America: metropolitan areas|publisher=World Gazetteer|year=2011|access-date=February 19, 2012|archive-url=https://web.archive.org/web/20070930223100/http://world-gazetteer.com/wg.php?x=&men=gcis&lng=en&dat=32&geo=-2&srt=pnan&col=aohdq&va=&pt=a|archive-date=September 30, 2007|url-status=dead}}</ref> 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 ([[Border checkpoint#Busiest checkpoints in the world|fourth-busiest]] overall). The city’s airport, [[San Diego International Airport]], is the busiest single-[[runway]] airport in the world.{{efn|[[Gatwick Airport|London-Gatwick]] and [[Mumbai International Airport|Mumbai International]], which both handle more traffic, each have two operational runways, though only one can be used at a time because of aircraft separation requirements (leading to these airports frequently being misleadingly referred to as “single-runway airports”).}}<ref>{{Cite web|date=2017-11-20|title=San Diego Int’l Airport will dig up the runway every night for a year|url=https://www.sandiegouniontribune.com/business/growth-development/sd-fi-airport-runway-digging-project-20171120-story.html|access-date=2021-01-26|website=San Diego Union-Tribune|language=en-US}}</ref>

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 Diego–Tijuana]] [[conurbation]], the second most populous [[transborder agglomeration|transborder metropolitan area]] in the [[Western Hemisphere]] (after [[Detroit–Windsor]]), home to an estimated 4,922,723 people as of 2012.<ref>{{cite book|url=http://world-gazetteer.com/wg.php?x=&men=gcis&lng=en&dat=32&geo=-2&srt=pnan&col=aohdq&va=&pt=a|title=America: metropolitan areas|publisher=World Gazetteer|year=2011|access-date=February 19, 2012|archive-url=https://web.archive.org/web/20070930223100/http://world-gazetteer.com/wg.php?x=&men=gcis&lng=en&dat=32&geo=-2&srt=pnan&col=aohdq&va=&pt=a|archive-date=September 30, 2007|url-status=dead}}</ref> 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 ([[Border checkpoint#Busiest checkpoints in the world|fourth-busiest]] overall). The city’s airport, [[San Diego International Airport]], is the busiest single-[[runway]] airport in the world.{{efn|[[Gatwick Airport|London-Gatwick]] and [[Mumbai International Airport|Mumbai International]], which both handle more traffic, each have two operational runways, though only one can be used at a time because of aircraft separation requirements (leading to these airports frequently being misleadingly referred to as “single-runway airports”).}}<ref>{{Cite web|date=2017-11-20|title=San Diego Int’l Airport will dig up the runway every night for a year|url=https://www.sandiegouniontribune.com/business/growth-development/sd-fi-airport-runway-digging-project-20171120-story.html|access-date=2021-01-26|website=San Diego Union-Tribune|language=en-US}}</ref>