Hartsfield-Jackson International Airport may be the world's busiest airport, but it came in second to Chicago O'Hare in a ranking of airports based on domestic connectivity.
There's a good reason why, and it has to do with where Atlanta is located and which airlines are the biggest operators at each airport.
The ranking by aviation intelligence firm OAG is based on the ratio of possible connections between domestic flights within three hours, relative to the total number of destinations served by the airport.
Hartsfield-Jackson has more domestic flying than O'Hare but fewer opportunities for connections between those flights, according to the study.
O'Hare has two major airline hubs, operated by American and United.
Atlanta's two largest airlines are Delta Air Lines and Southwest Airlines. Southwest, the second-largest carrier, does not operate a hub-and-spoke network, and at Hartsfield-Jackson focuses primarily on travelers from Atlanta or headed to Atlanta and not connecting.
Chicago has an advantage for domestic connectivity based on its central U.S. location, which makes it a particularly attractive place for a hub connecting domestic travelers going from east to west or vice-versa.
In contrast, airports in coastal locations "limit domestic connectivity options," and are more beneficial for international connectivity, according to OAG.
When it comes to international connectivity overall, London Heathrow was tops and Hartsfield-Jackson ranked 8th.
In the domestic ranking, behind O'Hare and Hartsfield-Jackson came Charlotte, Dallas/Fort Worth and Denver.
Megahubs "are critical to global airline efficiency and play an essential role in providing travelers with more options for ticket costs, flight frequencies and available destinations,” said OAG chief operating officer Mike Benjamin in a written statement.
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Airport’s Latin pitch: Come for the shopping Hartsfield-Jackson ranked 2nd for domestic connectivity between Chicago O'Hare, even though Atlanta has more domestic flying.