Quantifying geographic borders based on multi-scale human mobility

 

CHRISTIAN THIEMANN

ESAM, NORTHWESTERN UNIVERSITY, EVANSTON, IL

 

Geographic borders are not only essential for the distribution of administrative responsibilities and the allocation of public resources, they also influence the interregional flow of information, cross-border trade, the diffusion of innovation and technology, and the spread of infectious diseases. However, as increasing interactions and mobility across long distances, cultural, and political borders continue to amplify the small world effect and effectively decrease the relative importance of local interactions, it is difficult to assess the location and structure of effective borders that may play the most significant role in mobility-driven processes. The paradigm of spatially coherent communities may no longer be a plausible one, and it is unclear what structures emerge from the interplay of interactions and activities across spatial scales. Here we analyze a multi-scale proxy network for human mobility that incorporates travel across a few to a few thousand kilometers and determine an effective system of geographically continuous borders implicitly encoded in multi-scale mobility patterns. We find that effective large scale boundaries define spatially coherent subdivisions and only partially coincide with administrative borders. We find that spatial coherence is partially lost if only long-range traffic is taken into account. We introduce a technique that allows a new type of quantitative, comparative analysis of multi-scale interaction networks in general and may provide insight into a multitude of spatiotemporal phenomena generated by human activity.