WASHINGTON (AP) -- The city of light is also the city of flight, says a new study listing Paris as the most vital connecting point for international air travel.
Anchorage, Alaska, places a surprising second on the list, followed by London, Singapore and New York.
The connections among 3,883 communities with airports around the world were analyzed by a team of researchers led by Luis Amaral of Northwestern University. The results are being published in Tuesday's issue of Proceedings of the National Academy of Science.
The air transportation network is like the Internet, the study concluded, with networks and hubs funneling traffic around the world.
The findings are important in understanding the flow of travelers and in studying the potential movement of new diseases, Amaral said.
In addition, the analysis could help regulators determine airports where more competition is needed, and study of the network could even shed light on the functions of biological networks within the human body, according to Amaral, an associate professor in the Department of Chemical and Biological Engineering.
A traveler can get from any of the cities to any other with an average of 4.4 flights, and more than half the communities are connected with four flights or fewer, the researchers found.
The most difficult air route? Getting from Mount Pleasant in the Falkland Islands to Wasu, Papua-New Guinea, requires 15 separate flights.
The researchers found that the busiest locations are not always the most important for the network.
Anchorage, for example, has nonstop flights to 39 other cities, far fewer than the 242 cities connected to London nonstop.
But Anchorage edges London in a vital measure called centrality _ a rating of the shortest paths connecting any two cities that involve a transfer at a particular city.
It's centrality that boosts the importance of cities such as Anchorage and Port Moresby, Papua-New Guinea, which serve as connection hubs between many other airports and international connections, the researchers explained.
Alaska, for example, has many airports, but most connect only to other Alaskan airports. Only a few connect to the ''lower 48'' states. There are political constraints on flights directly between most of Alaska and Canada, even to cities close to the border.
Thus, getting from most of Alaska to somewhere outside the state often involves going through Anchorage, boosting that city's centrality rating.
Similarly, many Pacific islands are connected by air and Port Moresby is the hub that links lots of them to the outside, placing that community seventh on the worldwide list, behind Los Angeles but ahead of such busy places as Frankfurt, Tokyo and Moscow.
Paris and London benefit from their nation's colonial pasts, with many flights from Africa and Asia going to those cities, where travelers transfer to other planes to go on.
Indeed, they are the top cities in the world for nonstop flights to other places. Paris leads with flights to 250 other cities, followed by London, 242; Frankfurt, 237; Amsterdam, 192 and Moscow, 186.
The two busiest airports in the United States are in Chicago and Atlanta. The study ranked Chicago 13th on the worldwide centrality list and 6th for nonstop flights, with connections to 184 cities. Atlanta ranked 29th for centrality and 8th in connections, with flights to 172 cities.
The study analyzed 531,574 flights operated by 800 airlines worldwide from Nov. 1 to Nov. 7, 2000. While the data are four years old, the researchers say the current worldwide airport network is virtually identical to the one at that time.
The research was funded by the National Institutes of Health.