A Multi-Level Evaluation of the 3-30-300 Rule Using Individual- and Building-Level Analyses in the Japanese Urban Context: A Case Study of Himeji City

Abstract Background The 3-30-300 rule—ensuring 3 trees visible, 30% green cover, and access within 300 m to green spaces—has been proposed as a target to enhance the availability of ecosystem services from urban green spaces and trees. Although existing studies have examined how Western cities do not achieve this rule using aggregate data, which residential building and individuals in high-density East Asian cities benefit from the rule remains unclear. Methods This study aims to develop a method for evaluating the 3-30-300 rule at the individual level using synthetic population data and to clarify its impact on population groups across different residential building types and urban densities, as well as on groups with different attributes in Himeji City, Japan. Results The results show that, similar to other cities worldwide, only 5.1% of the population of Himeji City fully meets the 3-30-300 rule, with particular challenges in achieving 30% green cover. Apartments find it harder to meet the overall 3-30-300 rule, while residents in detached houses tend to have 30% green cover. Elderly groups tend to achieve 3 trees visible as well as 30% green cover. Conclusions The underlying mechanisms differ from those in Western cities and are likely influenced by the decline in privately owned trees, the role of street trees, and urban planning systems in park provision. The results enable a microscale visualization of environmental injustice, facilitating policy prioritization to allocate limited resources aligned with the 3-30-300 rule.