Robustness and Persistence in the Italian Urban Landscape

Local systems are conglomerations of municipalities held together by commuting links. ? Are they real life objects or the result of some cryptic algorithm? Real life objects. Real life cities, to be precise, even if not made of brick and mortar, but of relationships. Relationships is the matter cities are made of. ? Can you prove it? Not in the sense we can prove a theorem. But we can bring you convincing evidence based on natural experiments of history . Statistics Italy (Istat) has been disseminating local systems based on commuting data collected on the occasion of population censuses since 1971. Recently, it changed the algorithm generating local systems. This gives the opportunity for a three-way comparison between local systems geographies: * between the 2001 and 2011 results obtained with different algorithms; * between the 2001 and 2011 results obtained with the same (new) algorithm; * between the 2001 geographies resulting from the application of different (old and new) algorithms. This way, we can identify persistent local systems, those found by the same (new) algorithm both in 2001 and 2011; robust local systems, those identified in 2001 no matter which algorithm was used; local systems which are both robust and persistent, and so on. The main result, the one that proves the point that we were making above, is that out of 611 local systems, 503 are both robust and persistent. Many of them maintained the same name and are composed of the same municipalities; many others gained or lost municipalities, but still maintained their identity and their core. Those systems in 2011 account for 5,215 core municipalities and 47 million inhabitants, 79% of the total population of Italy. The remaining municipalities and systems are characterized by weak commuting links and either are located in remote areas or represent the contendible margins of strong systems.