Comparison of methods for green cover assessment: Options of aerial photography and satellite imagery in Japanese municipalities

Municipalities in Japan assess urban green space under their Master Plans for Parks and Open Spaces, often using green-cover percentage as an indicator. Yet, survey methods and definitions vary across cities, limiting the comparability of results. This study investigates the methodologies adopted by the 20 ordinance-designated cities, the rationales behind their choices, and the challenges of shifting between approaches. Questionnaire and interview data revealed three main sources of imagery—aerial photography, satellite imagery, and tax assessment photography—each reflecting trade-offs among cost, resolution, and continuity. Aerial survey costs were linked to coverage area, while satellite imagery costs correlated with resolution demands shaped by population size and fiscal capacity. Cities emphasized maintaining temporal consistency in data specifications to document long-term urban change. These findings clarify the methodological considerations underlying municipal green-cover surveys and provide guidance for balancing cost, accuracy, and continuity in urban green-space monitoring. • Many municipalities save costs by reusing aerial images for fixed-asset taxation. • The study found three types of data: aerial, satellite, and tax survey imagery. • Satellite costs depend on resolution, reflecting population and fiscal capacity. • Municipalities prioritize keep resolution consistent to align past surveys results. • Findings give municipalities insights to balance cost, data continuity, and accuracy.