Evolution of the periphery of a self-organized road network

Urban roads are geographical planar networks, making their growth patterns constrained over the available physical space. In this work, we quantify the center (core)-periphery structure of an urban road system based on the betweenness centrality of the nodes, and then measure their spread over the evolution of the urban zone. Using corrected and georeferenced historical maps of Manila, Philippines, we observe temporal invariance of the betweenness centrality distributions, along with the preponderance of comparable-betweenness node connections, both of which signify the preservation of the planarity of the network. Despite the geographical expansion of the road network, we observe topologically peripheral nodes in the geographical center for all the map periods considered, signifying the presence and growth of dendritic dead-ends which may ultimately affect the traffic flow. The shortest paths among the topological periphery shows an evolution towards a homogenized, grid-like structure for the entire network. Understanding peripheral connections, not only for planar networks but also for other complex networked entities, may hint at the efficiency of transport within the system, as these peripheral nodes represent the least “important” sites in the network.