Aging societies and population decline have been on the rise globally, but in Japan, the situation has exasperated tenfold. A staggering 36.21 million people, or 28.9% of the populace, are 65 and over. Further, 74.6% of Japan’s 1,747 cities are categorized as shrinking, with urban policies struggling to keep up with the decline. However, the factors that correlate with population changes in cities of varying sizes have not been clarified.

Dr. Haruka Kato, a junior associate professor at Osaka Metropolitan University, examined these multidimensional factors using the Economic, Social, and Educational (ESE) dataset, which is a cross-sectional dataset of 270 indicators of each Japanese city. This study used the machine-learning algorithm XGBoost, which analyzed the nonlinear relationships between the population change from 2005 to 2010 and the other 269 indicators.

The results revealed that most shrinking cities in Japan are medium-sized or small. Regarding the multidimensional factors, the rate of population change is strongly correlated with social-related indicators, such as changes among persons ages 0-14 in small cities, natural population change in medium-sized cities, and migration rates in large cities. Additionally, population changes correlated with the financial strength index as an economic-related factor in medium-sized cities. Furthermore, population changes correlated with the designation of underpopulated areas as an urban-planning-related factor in small cities.

“These results imply that urban policies should be designed according to the size of the city,” said Dr. Kato. “Medium-sized cities should effectively formulate policies other than urban planning, such as childcare initiatives that would contribute to improvements in natural population change and the financial strength index. Meanwhile, small cities need to consider designating underpopulated areas.”

The findings were published in Environment and Planning B: Urban Analytics and City Science.

Funding
Haruka Kato received funding from the Japan Society for the Promotion of Science (grant numbers 23K26284 and 24K17421).

Declaration of Conflicting Interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

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