Spatiotemporal changes of urban vacant land and its distribution patterns in shrinking cities on the globe.

Urban vacant land (UVL) has been an important issue in the urbanization process, especially for shrinking cities. Identifying UVL and analyzing its spatiotemporal characteristics are the foundation for coping with this issue. This study identified UVL in 497 shrinking cities on the globe (10 % of shrinking cities in total) in 2016 and 2021 using manual labeling and deep learning to reflect the distribution patterns of UVL and its spatiotemporal changes. The results reveal that a global expansion of UVL from 2016 to 2021 in 497 shrinking cities, with diverse distribution patterns and varying changes across different regions. As for socioeconomic factors, UVL is related to population shrinkage, and the UVL ratio presents a phased change with the increase of the urbanization rate, revealing an inverted U-shaped relationship between the UVL ratio and the urbanization rate. The distribution patterns of UVL also vary globally in different urbanization phases. This study can provide theoretical and practical insights for improving urban planning and promoting sustainable urbanization.