Urban Perforation and Regeneration in Japan: The relationship between Urbanization Characteristics, Network Centrality and Population Distribution

International audienceJapan experienced spectacular urbanization and population growths over the course of the last hundred years. With a population of 57,963 million of inhabitants in 1920, its count more than doubled when the population reached its highest level in 2010 with 128,057 million of inhabitants. These trends have been accompanied by a massive urbanization dynamic, massive to such extent that with an urbanization rate now reaching 93.0% (UN, 2014), the distinction between urban and rural spaces is becoming pointless. The Japanese system of cities is mostly made of a rather limited number of overlapping megapolises characterized by a hyper-dense population distribution. Japan is meanwhile also referred to as a post-growth society, being ahead of other developed countries in some sociodemographic and economic trajectories. Increased longevity combined with a very low fertility rate show that the population is expected to shrink by one-third by 2060, with a remaining count composed of a proportion of population aged 65 (or older) of at least 40% (IPSS, 2012). The interesting phenomenon is that the Japanese society is expected to keep urbanizing despites the population decrease (97.7% urban by 2050; UN, 2014). It thus presents new challenges, never seen before on such a large scale, regarding the spatial distribution and evolution of intra-urban population densities that are already in place. Dedensification leads to urban perforation, a process characterized by the concentration within metropolitan areas of vacant plots and buildings, store closures, etc. Conversely, perforations are accompanied by a density increase in others locations. Anticipating and planning a sustainable shrinkage, a successful regeneration and/or maintaining an equilibrium in some spaces has become a priority for the government