This study revealed the spatial patterns and temporal trends of numerical ageing, structural ageing, and four types of population ageing in Tokyo according to the distance from the city centre and the nearest train station. Three main patterns and trends emerged. First, the number of individuals in the older population was higher in grids closer to the JR Yamanote Line and to the nearest station, while the older adult proportion of the population was higher in the grids closest to and farthest from the JR Yamanote Line and the nearest train station. Second, in relation to distance from the JR Yamanote Line, accumulation grids and dilution grids were more prevalent within 40 km of the JR Yamanote Line. Decline and concentration grids were more prevalent at distances more than 40 km from the JR Yamanote Line, and the number of decline grids increased over time, while the number of concentration grids decreased. Third, regarding the types of ageing in relation to the nearest train station, accumulation and dilution grids were more prevalent within 1 km of the nearest train station, and the number of accumulation grids decreased over time while the number of dilution grids increased. Decline and concentration grids were more prevalent at greater distances from the nearest train station and their prevalence increased over time.

Spatial Patterns and Temporal Trends of Numerical Ageing, Structural Ageing, and Ageing Population Types in Relation to Distance from the City Centre

Both the number and proportion of the older adult population in Tokyo exhibited a concentric pattern. The number and proportion of the older adult population was highest in the city centre, lower toward the suburbs, and small in number but large in proportion in the mountainous areas. An east-west divide was also evident in both the number and proportion of the older adult population, which was related to Tokyo’s distinct geography. A larger number of individuals in the older population, but a smaller overall proportion, lived in the eastern part of Tokyo, where there is a concentration of businesses and residential areas. The western most part of the city is composed of several mountains with wild boars roaming freely around the area; hence, it is sparsely inhabited by the older population, although they were highly concentrated in terms of the proportion of the overall population.

Both the number and proportion of the older adult population exhibited a city centre-suburb divide. The number of individuals in the older population in Tokyo was higher in the city centre than in the suburbs. This spatial pattern is similar to that observed in Perth, Australia (Atkins & Tonts, 2016), and in regional cities in Japan, such as Sapporo, Sendai, Hiroshima, and Fukuoka (Feng, 2015). The difference in the numbers of individuals in the older population between the city centre and the adjacent suburbs decreased over time, which may indicate the movement of older members of the population toward the suburbs close to the city centre (Kikuchi & Sugai, 2018). The older adult proportion of the population was higher in the city centre and decreased toward the suburbs. The decreasing older adult proportion of the population from the city centre to the suburbs was consistent with the results of Naganuma et al. (2006) in 2000 and Wakabayashi and Koizumi (2018) in 2005. The general pattern of a higher older adult proportion of the population living in the city centre than in the suburbs was also similar to the pattern observed in Beijing, China, but it contrasted with cities in Europe, such as Milan, Madrid, Berlin, Brussels, Dublin, Amsterdam, London, Lisbon, Copenhagen, and Paris (Arup et al., 2015). Considering the metropolitan areas in OECD member countries, the older adult proportion of the population living in metropolitan areas in Japan, Korea, Mexico, and the United Kingdom was smaller in the urban core (densely inhabited areas) than in the hinterlands (defined as the worker catchment area outside the urban core) in 2001. This contrasted with the results of this study, which may imply that Tokyo’s spatial pattern may also be different from other metropolitan areas in Japan. Notably, the older adult proportion of the population in the city centre and the suburbs was almost the same in 2015. This may indicate a movement of the young population toward the city centre and suburbs, or a movement of the older population to the suburbs.

The distinct spatial patterns in the different types of ageing were related to the geography of Tokyo. Accumulation was prevalent, but it decreased over time in the city centre along with an increase in dilution and decline. Accumulation remained high in the suburbs and this trend did not change substantially over the 15-year study period. Decline and concentration mainly occurred in the mountainous areas. These patterns and trends imply that ageing in Tokyo is more diverse and dynamic in the city centre than in the suburbs and mountainous areas. In comparison with Atkins and Tonts (2016), the spatial patterns of the types of ageing in Perth, Australia, were quite different from the spatial patterns in Tokyo. In general, different types of ageing occurred in the suburbs of Perth compared to the city centre. Accumulation, concentration, and dilution occurred in the suburbs, while decline occurred in the city centre. The older population in Perth increased over time in the suburbs where there have been recent subdivision developments and the construction of a commuter railway (Atkins & Tonts, 2016).

The ‘Back to the City Centre’ phenomenon had a major impact on the structure of ageing in Tokyo after the bubble economy ended in the 1990s. During its economic boom, the Tokyo Metropolis experienced a substantial increase in land prices in the city centre (PwC Japan Group, 2016). New towns were then developed in the western suburbs of the Tokyo Metropolis to provide reasonable housing (OECD, 2015). This development triggered an outflow of people to the suburbs, including large cohorts of young families; the outflow led to an increase in the proportion of older people in the city centre. When the bubble economy ended in the 1990s, land prices began to decline in Tokyo’s city centre, which resulted in changes in land use (Doteuchi, 2003; Tsubomoto & Uozumi, 2012). To revive the city centre, a massive redevelopment of the business, shopping, and entertainment districts occurred throughout the 2000s, along with the construction of condominiums and public housing complexes, as part of the ‘Urban Renewal’ program (Doteuchi, 2003; PwC Japan Group, 2016; Yabe, 2018). This program encouraged both older adult and young populations to reside in the city centre because of the convenient lifestyle (Kikuchi & Sugai, 2018; Yui et al., 2017). The resulting population shift is reflected in the increasing occurrence of dilution in the city centre along the JR Yamanote Line. In some areas of the city centre, changes in land use subsequently displaced the residents, including the older population, thus contributing to decline (Tsubomoto & Uozumi, 2012). The ‘Back to the City Centre’ phenomenon also affected the attitude of the young population; notably, it attracted young families toward city-centre living. More young workers, especially professional workers, chose to live in the 23 wards of Tokyo rather than move to the outer suburbs (Yabe, 2018). Young families with fewer children also remained and raised their children in the city centre rather than buying a house and settling in the suburbs, as their parents had tended to do (Yabe, 2018; Yui et al., 2017). These changes in attitude led to population shrinkage in some areas outside the city centre (Yui et al., 2017). The older population chose to age in place while the younger population moved out of the suburbs, leading to accumulation in the suburbs (Naganuma et al., 2006; Yui et al., 2017). Because the internal migration mobility of the older population in Japan is generally low, the size of the ageing population in the suburbs will likely increase in the future.

In the mountainous areas in the westernmost part of Tokyo, depopulation has been occurring since the 1980s because of the decline in the local timber market (Nishino, 2007). The older adults who remain have chosen to age in place. The resulting trend is reflected in the concentration and decline observed in this area. This indicates that the older population, although it was small, lived in disadvantaged areas, making them more vulnerable. There is a need to ensure that the older population in these areas are not ‘left behind’ in terms of living conditions, health, and other services.

Spatial Patterns and Temporal Trends of Numerical Ageing, Structural Ageing, and Types of Population Ageing in Relation to Distance from the Nearest Train Station

The results indicated that areas with a high number of older adults in the population, and areas with relatively small proportion of the older adult population, were both located within a walkable distance of the train station. These findings are consistent with the World Health Organization (2015) recommendation that the older population should have access to public transportation within a walkable distance of 500 m from home.

Together, the trends in the number and proportion of the older adult population showed that although the number of individuals in the older population increased over time in areas within 4 km of the train station, the older adult proportion of the population increased in areas far from the station (> 2 km). This may indicate that a younger population is moving into areas near to train stations, while the older population is ageing in place within areas far from the stations. Ito et al. (2011) showed that, compared with France and Germany, the older population in regional cities in Japan tended to live in areas where the frequency of train services was low and in areas far from train stations, where transportation was difficult and inconvenient to access. According to Ariga and Matsuhashi (2016), the majority of the older population in Tokyo Metropolitan Area in 2010 had no adequate train access, meaning they were living more than 1 km from a train station.

As discussed earlier, there was a redevelopment program in Tokyo city centre in the 2000s, mostly near to the train stations, which has had an impact on the structure of ageing. The movement of the young and older population into condominiums and housing complexes constructed near train stations reflects the occurrence of accumulation and dilution within 1 km of train stations. On the other hand, the ageing in place of the older population in the suburbs and mountainous areas, where train density is lower, reflects the high occurrence of concentration and decline more than 8 km from the nearest train station.

Policy Implications

Our findings have several policy implications. Because changes in the ageing population will likely alter local needs across the city, the locations and supplies of urban infrastructure and the levels of public service provision must be adjusted (OECD, 2015). For example, different ageing types exist in the city centre; therefore, these areas will likely experience increased demands for services and infrastructure related to both young and old populations. Local governments must determine how to maintain good levels of various services and infrastructure to meet the needs of both populations (OECD, 2015). In suburban municipalities, ageing accumulation occurred within most areas. Suburban spatial structures are car-dependent because of low train station density, the presence of detached housing and medium-rise residential housing on steep terrain, and the placement of services far from communities (Doteuchi, 2003; Yui et al., 2017). As the numbers of older people increase in these areas, there is a need for local governments and the private sector to improve transportation, provide age-friendly housing, and develop compact city strategies (OECD, 2015). In mountainous areas, as the numbers of older adults decrease and their geographic distribution becomes sparse, local governments will experience increasing costs in terms of service provision. Cooperation among neighbouring municipalities, the private sector, and local communities is needed to jointly provide services and reduce costs, thereby ensuring that no one is ‘left behind’ (OECD, 2022).

In Japan, a ‘Community-based Integrated System’ was implemented to provide integrated and comprehensive care services at the community level; this system facilitates ageing in place with cooperation from local residents (Tsutsui, 2014). The identification of different ageing types at the neighbourhood level may guide local governments in the efficient implementation of this system based on local needs. For example, in municipalities with high ageing accumulation and concentration, there may be small numbers of local young volunteers to care for the older population. Local governments may need to provide strong support to older people who care for other older people; they may also need to ensure strong cooperation from the private sector and non-profit organisations (Japan International Cooperation Agency (Japan International Cooperation Agency [JICA], 2022; Tsutsui, 2014). In areas with broader ageing distributions, an integrated care system that caters to all generations may be necessary to provide sufficient support to the community (JICA, 2022).

Limitations

This study had some limitations. First, some grids had inconsistent population data, such as a higher older population than the total population, and were therefore excluded from the study. However, this only represented 0.5% of the total number of grids. Second, because we did not have information for the exact location of the older adult population in each grid, we used the centroid of each grid to denote their location. We used a fine resolution 500-m grid as the unit of analysis, and for the purpose of our study this level of accuracy was considered sufficient. Third, we did not conduct a scale sensitivity analysis although our spatial analysis was sensitive to the scale of aggregation. However, Shiode et al. (2014) also observed that a 500-m grid was adequate to provide information on urban ageing. In future studies, a sensitivity analysis should be conducted to determine whether the results are consistent at different spatial scales.