This post is inspired by my Spring Break trip to Europe. Anyone who flew out of the northeast the Friday before break probably experienced the same headaches I did due to canceled flights, long delays, and generally unhappy and unhelpful airline service reps. I figured that storms were a common problem for airlines and was surprised that they didn’t have a better plan for handling the backups and delays. It made me think of the network infrastructure of airlines. Here is a study by the National Academy of Sciences on the worldwide air transportation network, its structure, and the roles of different types of cities.

To briefly summarize their findings, they saw that this network is a small-world network and “the most-connected cities are not necessarily the most ‘central’… this surprising result can be explained by the existence of several distinct communities.” These communities seemed to be based on a few factors, namely population density, economic development, and state and geographical borders. A few ideas stick out in this paper as being relevant to our coursework. For instance, the paper discusses the clustering coefficient, “the probability that two cities that are directly connected to a third city also are directly connected to each other.” This is similar to the phenomenon of social closure. They also come to the conclusion that connectedness and centrality do not necessarily imply one another by analyzing the betweenness of cities in the network and noticing that cities with low degree (not hubs) sometimes have large betweenness values. “Although the most connected cities are located mostly in Western Europe and North America, the most central cities are distributed uniformly across all of the continents.”

This could explain the huge delays that occur when a site that connects two major communities shuts down. These sites are usually very central and without them the entire network experiences delays costing enormous amounts of money each year. This article is more pertinent to the material from earlier in the course, but it still is a good example of an application of the material we’ve studied.