The continuous built-up area extracted from ISS night-time lights to compare the amount of urban green areas across European cities

The presence of urban green areas significantly impacts urban inhabitants' well-being. However, comparative studies across European cities are constraint by urban administrative boundaries, which commonly do not match the continuous built-up urban area. This makes comparative research on environmental indicators very problematic, as administrative boundaries are not usually appropriate to define the urban human environment. Therefore, this study aimis to explore the use of night-time light (NTL) images of the International Space Station (ISS) to delineate the continuous built-up area (CBA) of selected European cities to calculate the urban green area share per alternatively derived city extent. The result of the CBA shows that NTL images provide a robust data source to make the urban extent of European cities comparable. By comparing results of different datasets on green areas, we discuss the limitations of existing indicators and opportunities for new ones. Results show that green areas are rarely in close proximity to human living environment, even though the share of urban green areas within the CBA might be larger, as in comparison to the administrative boundary. We conclude that ISS NTL imagery is very suitable for mapping the CBA when aiming at comparability of environmental indicators across cities.