Percolation Model to Capture Urban Coalescence («Natural Cities»). The Case of Italy

The contribution intends to explore a new method to perimeter and identify urban areas based on a percolation model. Starting from the analysis of the road network and its nodes, through the application of some percolation measures it allows to identify different levels of urban agglomeration. The centrality of the road network is considered the primary indicator for understanding the urban agglomeration pattern. The simulation is applied to whole Italy. The simulation results are then compared with data from other sources of mapping urban regions, such as satellite lights and the degree of urbanization from the JRC GHSL. The correspondence between these mappings and the one obtained with the percolation model is analyzed and the rank-size distribution of the “natural cities” thus obtained is observed. The purpose of the contribution is to find and experiment a spatial searching method that allows us to identify the different shapes and sizes of contemporary settlement, regardless of the definitions that can be derived from administrative boundaries. The hypothesis is that the conurbations of contemporary settlement tend to merge and fragment in a dynamic process of continuous evolution, caused by the fact that urban limits follow flows and networks, without regard for historical administrative boundaries.