Underground space use of urban built-up areas in the central city of Nanjing: Insight based on a dynamic population distribution

With the expansion of cities and the emergence of various urban problems, urban underground space has been developed as a solu-tion. In China's urban transition context, there is a need for the development of underground space in urban built-up areas. In this case -study of the central city of Nanjing, we used spatial analysis and statistical methods to characterize the underground space use of urban built-up areas from a dynamic spatiotemporal perspective. We first analyzed the relationship between the population distribution and the underground space use of the central city of Nanjing based on a Baidu heat map, which can reflect the real-time population distribution, and then, we explored the spatiotemporal characteristics and spatial structure of the underground space use in urban built-up areas. The analysis results provide a reference for planning to improve and optimize the layout of underground space in the central city of Nanjing and, more generally, for the stock-type planning of underground space in urban built-up areas.