Recent Changes in Spatial Population Distributions within Municipalities in the Tohoku Region, Japan

Spatial population distribution changes within municipalities between 1995 and 2020 in the Tohoku region (Aomori, Iwate, Miyagi, Akita, Yamagata, and Fukushima prefectures) are examined. Using 4th mesh data from the Population Census of Japan to estimate the populations of central and peripheral areas of municipalities, municipalities are categorized into four types: absolute concentration, where both a central area's population and its percentage within a municipality increase; relative concentration, where a central area's population decreases, but its percentage increases; relative dispersal, where a central area's population increases but its percentage decreases; and absolute dispersal, where both a central area's population and its percentage decrease. Geographical patterns of these types are analyzed, as well as the relationships between these types and the municipal typology of Urban Employment Area (Large Urban Core Areas (LUCA), Large Urban Suburb Areas (LUSA), Small Urban Core Areas (SUCA), Small Urban Suburb Areas (SUSA) and Outside of Urban Employment Areas (OUEA). The main results are as follows. First, while the populations of all prefectures and most municipalities have declined since 1995, they tend to be concentrated in Miyagi Prefecture at a prefectural level and in prefectural capitals and their surrounding municipalities, as well as in cities with relatively large populations and their surrounding municipalities at a municipal level. Second, in most municipalities, population tends to be concentrated in the central area of a municipality. Most of these municipalities are of the relative concentration type and are found in OUEAs, SUSAs, and LUSAs. It is highly likely that spongification—sporadic population and household loss from residential areas—occurs throughout these municipalities because it is difficult to assume that the population concentration in a central area through relocation from peripheral areas to the central area has been achieved, given that the social growth rate is negative in both central and peripheral areas. Third, many municipalities of the absolute concentration type are located in LUCAs, LUSAs, SUCAs, and SUSAs, and both social and natural growth rates at the centers of these municipalities are positive. Fourth, most municipalities with absolute dispersion are found in LUCAs, LUSAs, SUCAs, and SUSAs. Among them, there are those with a doughnut-shaped distribution of population concentration areas due to a degradation or hollowing out of the city center, and these municipalities are classified as a type of relative concentration when the coverage of the central area is expanded. These municipalities include those that provided higher-order central location functions, that is, LUCAs and SUCAs. Although it has been argued that population tends to be concentrated near the center at a metropolitan level, it is not necessarily concentrated in the central area of a municipality at a sub-municipal level. Fifth, the natural growth rate of central and peripheral areas has decreased in all types of municipality in recent years, and its contribution to the population growth rate has tended to increase. In contrast, the social growth rate is highly correlated with regional differences in the population growth rate. Based on these results, it can be concluded that spongification occurs in a wide range of areas of the Tohoku region, whereas, simultaneously, population tends to be concentrated in areas that provide relatively higher-order central functions.