The impact of progressive liberalization on the spatiality of airline networks: a measurement framework based on the assessment of hierarchical differentiation

There seems to be a renewed trade-off between processes of concentration and dispersal in airline networks. This development calls for a framework that allows for a systematic assessment of the overall evolution of the spatiality of airline networks. To this end, we develop an analytical framework based on a set of spatial interaction indices, which allows measuring the degree of hierarchical differentiation (i.e. dominance and connectivity) in a network. Moreover, a normalization of these indices through a systematic comparison with the corresponding values for a rank size distribution makes it possible to engage in meaningful longitudinal analyses and/or to compare the spatiality of networks with different numbers of nodes and/or links. Our framework is tested by applying it to data on air passenger flows within Europe, and its usefulness is discussed in the context of research on air traffic liberalization.