Delineating functional regions from road networks: The case of South Korea

We apply a percolation method to South Korea’s road networks and identify major urban clusters. The results show that Korea has developed a highly mono-centric spatial structure, in which the Seoul Metropolitan Area expands to northern Chungnam, far beyond the limits conventionally assumed. A percolation threshold of 1080 m is critical in delineating Korea’s functional regions, and the results at this threshold show great similarity to flow-based maps. Similar model outputs support the percolation approach as an alternative to conventional flow-based methods. The similarity is higher for larger clusters, where the supply of road infrastructure better meets demand thanks to size-biased public resource allocation. Also, the similarity between model outputs tends to increase with a time lag, since road network configurations take time to catch up with the demand revealed in traffic flows. These findings speak for the need for increased connectivity in Korea’s smaller cities.