Key Points

◆Many municipalities are devising ways to mitigate economic constraints by utilizing aerial photographs for fixed-asset taxation as a cost-effective means.
◆Three types of data used for green-cover surveys are: aerial photography, satellite imagery, and tax assessment photography.
◆The cost of obtaining satellite imagery varies depending on the required resolution, reflecting differences in population size and fiscal capacity.
◆The municipalities’ selection of data is strongly influenced by geographic and socio-economic conditions, which shape the balance among three key factors: cost, accuracy, and data continuity.

Summary

　In Japan, municipalities use the Master Plan for Parks and Open Spaces as a basis for understanding and evaluating urban green environments, with the green-cover ratio—the proportion of land surface covered by vegetation—serving as a core indicator. The green-cover ratio is essential for assessing the environmental quality of cities and the health of ecosystems, and it is globally recognized as a key indicator of sustainable urban development. However, the types of imagery used, the definitions of “green” and “green area,” and the analysis methods employed for surveys vary across municipalities, making it difficult to ensure consistency and comparability between cities and over time.
　This study, focusing on 20 ordinance-designated cities in Japan, aimed to clarify the classification of green-cover ratio survey methods, the rationales behind their choices, and the challenges associated with transitioning between different approaches. Based on questionnaires and interviews with municipal officials, three main categories of the survey categories were identified:
(1) aerial photography specifically for green-cover surveys;
(2) aerial photography originally captured for tax assessments; and
(3) purchased satellite imagery.

　These survey methods reflected trade-offs among cost, resolution, and data continuity, revealing a range of choices made according to each city’s characteristics and fiscal capacity. Notably, utilizing aerial photographs originally captured for tax assessment purposes was shown to reduce survey costs significantly. However, several municipal officials noted challenges such as seasonality—using winter imagery for green cover assessments—as well as issues of comparability and consistency with past aerial photographs. Whether this approach can serve as a practical, cost-effective strategy balancing accuracy and expenditure remains a topic of growing interest.
　Analysis of the questionnaire and interview results revealed that survey costs tended to increase in proportion to the area surveyed in cities using aerial photography, whereas costs varied according to population size in those using satellite imagery. Furthermore, many municipalities viewed green-cover surveys not merely as quantitative assessments but as a means of documenting long-term urban changes, emphasizing the importance of maintaining methodological consistency to ensure comparability with past surveys.
　Moreover, it became clear that survey methods are not standardized and depend heavily on each municipality’s administrative capacity, financial resources, and prior practical experience. Therefore, when formulating future policy support and guidelines, a flexible approach tailored to local conditions will be required to strike an appropriate balance between cost efficiency and accuracy.
　In recent years, increasing attention has been directed toward satellite-based monitoring, supported by improvements in image resolution and the growing availability of web-based analytical platforms. However, transitions from aerial photography to satellite imagery have often been constrained by difficulties in maintaining consistency with previous datasets and by limited expertise in handling satellite data. Strengthening inter-municipal collaboration and knowledge sharing could serve as effective measures to address these challenges.
　The 20 ordinance-designated cities surveyed in this study were relatively large in population and possessed high administrative capacity. Metropolitan areas with extensive urbanized land tended to prioritize data continuity and high-resolution monitoring, whereas cities with extensive forest cover faced challenges related to seasonal variations in aerial imagery. In contrast, smaller municipalities tended to prioritize cost considerations. These regional variations suggest that while trends of cost, accuracy, and data continuity are broadly shared, the balance among these factors are strongly influenced by local geographic and socio-economic conditions.
　This study clarifies the diverse conditions surrounding green-cover surveys in Japanese cities, organizes their methodological background, and suggests pathways toward more effective and sustainable green-space monitoring. Future efforts should aim to broaden the scope of analysis to include small and medium-sized municipalities, evaluate the technical accuracy of survey methods through standardized validation, and introduce emerging remote-sensing technologies. Furthermore, collaborative surveys involving multiple municipalities, together with the establishment of shared data platforms, could serve as effective means to complement limited human and financial resources.
　These findings are expected to provide practical guidance for municipalities seeking to balance cost, accuracy, and data continuity, while also offering valuable insights for the formulation of future urban green space policies and the development of a standardized national monitoring system.

Figure 1　Changes in data selection for urban green-cover surveys by city.

　This study was supported by JSPS KAKENHI (JP22H03852, JP23H01584, JP23H03605, 25K15570), the JST Program for Co-creation in Knowledge Integration (JPMJPF2110), and the Environment Research and Technology Development Fund (JPMEERF20241M03) of the Environmental Restoration and Conservation Agency, provided by the Ministry of the Environment, Japan.


◆Related Links:Vegetation Cover Survey Methods at Cross-Roads: Choice of Aerial Photography or satellite imagery by Japanese Municipalities

Authors

Yuki Sofue, Assistant Professor
Faculty of Science, Department of Chemistry, Biology, and Environmental Science, Nara Women's University

Rintaro Shimazu, Master’s Program Student
　Laboratory of Forest Landscape Planning and Design, Graduate School of Agricultural and Life Sciences, The University of Tokyo
Ryo Kohsaka, Professor
　Laboratory of Forest Landscape Planning and Design, Graduate School of Agricultural and Life Sciences, The University of Tokyo

Paper Information

Journal:　Environmental and Sustainability Indicators
Type:　Original Research Article
Title:　Comparison of Methods for Green Cover Assessment: Options of Aerial Photography and Satellite Imagery in Japanese Municipalities
Authors:　Yuki Sofue, Rintaro Shimazu, Ryo Kohsaka* (*corresponding author)

Contact

The Laboratory of Forest Landscape Planning and Design, Department of Forest Science, Graduate School of Agricultural and Life Sciences, The University of Tokyo
Tel:03-5841-5218
E-mail: kohsaka.lab[at]gmail.com
(Please replace [at] with @ when contacting.)