Study on the spatiotemporal evolution of urban spatial structure in Nanjing's main urban area: A coupling study of POI and nighttime light data

The urban spatial structure reflects a city's development history, cultural heritage, and socio-economic conditions. A rational urban spatial structure is crucial for urban development. This study focuses on the main urban area of Nanjing, analyzing POI and nighttime light data from 2016 to 2020. Utilizing kernel density estimation and coupling coordination models, it explores the temporal and spatial evolution characteristics of Nanjing's urban spatial structure. Geographic detectors are employed to assess the impact of various factors on this structure. The findings indicate that: (1) Nanjing's urban spatial structure displays a pattern of central aggregation and peripheral expansion, with high brightness concentrated in the urban center and a significant increase in peripheral brightness, signaling initial success in establishing urban subcenters; (2) The coupling relationship between nighttime light brightness and POI density has strengthened, suggesting improved coordination of the urban spatial structure; (3) The evolution of Nanjing's urban spatial structure results from the combined effects of multiple factors, including economic level, population distribution, transportation conditions, and policy planning.