Denver International Airport (IATA: DEN, ICAO: KDEN), commonly known as DIA or DEN, serves as the primary airport for the Front Range Urban Corridor surrounding Denver. DIA is east-northeast of the Colorado State Capitol. DIA is the 20th busiest airport in the world and ranks 5th in the United States, with 64,494,613 passengers passing through it in 2018. It covers more than , making it the largest airport by land area in the United States and larger than the island of Manhattan. Denver serves as a major hub for United Airlines, is the headquarters and primary hub for Frontier Airlines, and is a major focus city and the fastest-growing market for Southwest Airlines.