Worldwide air transportation networks: a matter of scale and fractality?

In this study, we take a new view on air transportation networks, inspired by the physical concept of fractality. While other studies analyze networks individually, we aim to provide a unified understanding of the transitions among network layers. As a case study, we investigate the worldwide air transportation networks for the year 2015. We derive aggregated network instances at six different levels: airports, cities, spatial distance 100 km, spatial distance 200 km, regional network, and country network. While few nodes are important at all levels of aggregation, others only become important for few aggregation levels. Fractality analysis highlights that, as one moves from finer granularity to more coarse aggregation level, the network becomes denser but with fluctuating assortativity patterns; and that the modularity and the number of communities both decrease slightly. Networks at higher aggregation levels are more robust than the fine-grained counterparts, airport and city networks.