Vegetation cover survey methods at cross-roads: Choice of aerial photography or satellite imagery by Japanese municipalities

In Master Plan for Parks and Open Spaces (or Midori-no-Kihonkeikaku), municipalities delineate their future visions, goals, and strategies for the conservation and promotion of green areas. Regular surveys are typically conducted, especially in densely populated urban areas, to assess and monitor these green areas. However, the data collection approaches are not standardized and left to the discretion of each municipality, considering factors such as cost, effort, desired accuracy, and comparability with historical data. Consequently, the data published by various municipalities lack uniformity, complicating comparisons and a comprehensive understanding of the situation. Furthermore, the rapid advancement in image analysis technology has placed municipal survey methods in a transitional phase. This study targeted 20 special status cities, called “ordinance designated cities” in Japan, to ascertain the current state of vegetation cover surveys method in each city. Interviews were conducted with ordinance designated city from 30th May to 2nd June. As of 2024, eight ordinance designated cities utilized aerial photography and nine used satellite imagery to measure vegetation cover, indicating a nearly equal distribution. Additionally, three cities did not measure vegetation cover. Most cities had not altered their survey methods, but those that did primarily cited cost as the driving factor, with many transitioning from aerial photography to satellite imagery. This shift raised concerns about the consistency of past and future data, underscoring the need to develop methods for integrating data with varying resolutions and coverage areas.