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Throughout recent years, air travel and globalization have become more and more co-dependent. As revenues have increased worldwide since the 1970s, so has international (and intra-national) air flows. As American and European markets reach maturity, developing countries are experiencing strong growth rates in air traffic. The increase in airline connectivity across the world highlights how geographical and spatial constraints to moving people, knowledge and goods are gradually lifted. New technologies and high-speed rail networks usually relied upon to predict a decrease in the need for air travel have had opposite effects: air travel remains the preferred mode of travel of businessmen still requiring face-to-face contacts. The facts show that globalization increases global air transport while it is falso facilitated through the same airline flows.

Global cities are constituted by the flows of information, knowledge, money and culture passing through them rather than what they stock. Airline flows, taken to as representatives of infrastructure and communication networks, have therefore been used to determine the spatiality of the global city network. Such employment of the data is premised on the theories of Sassen and Castells and the importance of relations between cities. However, whereas data on cities is already sparse, relational data is sparser still. Air passenger flows therefore serve as valuable proxies for estimating relationships between cities. It is thought airflows reveal the international character of cities and the spatial pattern of global cities by providing resources to global processes (Cattan 1995; Derudder and Witlox 2005; Derudder et al. 2008). “The global airline network is a principal channel for the flows that define the architecture of urban connections” (Derudder and Witlox 2008: 75).

Derudder relies upon the ICAO data for 1998 to measure inter-city flows based on international air travel. Airports are aggregated when cities have multiple airports and cities are chosen when their traffic volume exceeds 5 million world load units. Using social network analysis, the author produces a ranking of the 57 most connected cities in the world economy.