Small Worlds in Air Transportation

There is a fascinating new “small world” study out in the Proceedings of the National Academy of Sciences. It looks at small world phenomena in the context of global air transportation i.e, which cities are most central, and which cities are most connected. The results, as this table shows, are somewhat surprising:

We analyze the global structure of the worldwide air transportation network, a critical infrastructure with an enormous impact on local, national, and international economies. We find that the worldwide air transportation network is a scale-free small-world network. In contrast to the prediction of scale-free network models, however, we find that the most connected cities are not necessarily the most central, resulting in anomalous values of the centrality…

Anyone care to hazard a guess, without reading the paper, why some of the most central cities in the global air transport network are not the most connected? By way of context, such is not the case in other scale-free networks, like the Internet, where centrality and connectedness go hand-in-hand.


  1. A shot in the dark here, but I’d suspect these were hubs or deployment posts for military operations – perhaps even places where the US established foreign bases.
    There was likely some kind of other reason why these places were first developed, and traffic continued to flow through them more based on legacy infrastructure rather than business logic. Its notable that Memphis, the centre of gravity for Fedex is not even on the list. But its not surprising given that its landlocked.
    Regards from BC