Community Structure in Multi-Scale Transportation Networks

Large scale communities and their geographical boundaries are key determinants of various human mediated spatially extended dynamical phenomena. The geographic spread of emergent human infectious diseases such as SARS (severe acute respiratory system) and human influenza A are prime examples.

However, the quantitative impact of large scale community structures and their boundaries is difficult to assess. In this project we investigate the network of human traffic between the counties in the US. The aim of this study is to determine effective large scale communities and see whether these do or do not coincide with historically evolved political boundaries.

Figure 1: Based on the wheresgeorge.com network, 11 large scale communities in the US can be identified.

As a follow up to a previous project (The scaling laws of human travel) we employ the geographic circulation of individual dollar bills as a proxy for human traffic. The data was collected at the online bill tracking portal www.wheresgeorge.com.

In this study we use trajectories of over 11 million dollar bills to estimate the traffic between approx. 3000 counties in continental United States. We develop and employ algorithms for optimal modulariy computation in strongly heterogeneous complex networks.