Characterizing urban actively populated area growth in the Yangtze River Delta using nighttime light data

Understanding the spatiotemporal evolution of urban actively populated area (UAPA) in urban agglomerations is crucial for sustainable development. This study fills a gap in previous research that overlooked urban population dynamics, leading to inaccurate UAPA characterizations. We utilized nighttime light (NTL) data, which reflects both urban construction status and population dynamics, to characterize UAPA growth pattern in the Yangtze River Delta. We developed a novel search method for extracting UAPA that demonstrated greater accuracy and adaptability than traditional threshold method. We employed expansion rate (ER) and annual growth rate (AGR), and a method for recognizing urban expansion patterns, to illustrate the characteristics and spatial changes in the Yangtze River Delta. We divided the research stage (1992–2019) into six stages based on China’s Five-Year Plan. The results demonstrated that the UAPA size at the end of the sixth stage (2016–2019) was about 6 times greater than that at the end of the first stage (1992–1995). The ER and AGR were approximately 15% during the first stage (1992–1995), and dropped dramatically following the fourth stage (2006–2010). Edge expansion is a typical predominant spatial expansion pattern for UAPA. While the proportion of patches with newly generated expansion showed an initial upward and then a downward trend, the percentage of patches with infilling expansion exhibited a pattern of first decreasing and then increasing. This study aims to provide support for future development planning and policy formulation.