The Relative Index of Metropolisation of the Territory: Quantifying spatial reorganisation driven by land-based transport

The evolution of transport networks and modes drives dynamics of spatial reorganisation that facilitate the process known as territorial metropolisation, understood as the progressive integration of fragmented territories into operationally connected systems. The reduction of effective distances induced by transport infrastructures leads to improvements in mobility and accessibility which, from a functional perspective, translate into a theoretical compaction of territory and an increase in the intensity of socio-economic interactions. Despite its conceptual and empirical relevance, to date there has been a lack of a precise and objective quantitative measure capable of systematically characterising this functional compaction and reinforcing its significance as a key element of spatial reorganisation and, more broadly, of territorial metropolisation. This article presents the Relative Index of Metropolisation of the Territory (RIMT), a methodology designed to quantify this compaction induced by land-based transport infrastructures. The index is based on travel times between nodes and geometric techniques easily implementable in GIS environments, yielding a replicable, comparable measure free from parametrisation bias. The utility and scope of the RIMT are illustrated through four case studies: the road network in southern Michigan, the Haramain High-Speed Railway in Saudi Arabia, the Shinkansen network in Japan, and a prospective exercise concerning a Hyperloop network in Europe. The results show significant theoretical compaction of the connected surface (with values ranging from 72.2% to 98.2%), consistent with Tobler’s First Law of Geography, which links proximity to greater socio-economic interaction. The RIMT is proposed as a complementary resource to established territorial assessment tools, providing an explicit spatial dimension that enriches the analysis of the socio-economic impacts associated with land-based transport networks, and offering an additional tool for planners, policymakers and funding bodies.