San Francisco International Airport — San Francisco, United States

San Francisco International Airport, built out on landfill along the edge of San Francisco Bay well south of the city itself, serves as United Airlines' largest hub and one of the principal gateways connecting the United States to East Asia and the Pacific Rim. Fog rolling in off the bay has historically caused some of the most persistent weather-related delays in American commercial aviation, a quirk of SFO's closely spaced parallel runways that air traffic planners have worked for years to mitigate through new procedures and infrastructure investment. The airport's Terminal 1, renamed in honor of gay rights leader Harvey Milk, reflects San Francisco's civic identity, while an on-site aviation museum and rotating art exhibitions give the terminals a distinctly cultural character uncommon among major airports. Silicon Valley's technology industry generates outsized business travel demand through SFO, reinforcing its role as one of the busiest and most economically significant airports on the West Coast.