Hartsfield-Jackson Atlanta Airport

Hartsfield-Jackson Atlanta International Airport (ATL) is the busiest airport in the world by passenger traffic, a title it has held almost every year since the late 1990s, moving well over 100 million passengers in a typical year. Its dominance comes less from Atlanta's size than from its geography and its role as the principal hub of Delta Air Lines: it sits within a two-hour flight of most of the U.S. population, making it the natural place to change planes.

Built on the idea of the connecting hub, the airport funnels travelers through a central terminal and a long spine of parallel concourses linked by an underground train, a layout widely copied around the world. So many journeys pass through it that an old Southern joke holds that "whether you are going to heaven or hell, you have to change planes in Atlanta." It is one of the largest employers in the state of Georgia.