Spatio-Temporal Evolution Features and Impact Factors of Urban Expansion in Underdeveloped Cities: A Case Study of Nanchang, China

Studying the expansion of urban construction land is necessary to promote rational land use and scientific territorial spatial planning. To reveal urban built-up areas, this study uses 1990–2020 Landsat remote sensing images, superimposed with NPP/VIIRS nighttime light. To extract urban construction land, support vector machines are then used to conduct classification experiments. The spatial-temporal features are analyzed using the expansion index, the shift of the center of gravity, and expansion direction, while influencing factors are analyzed using a Geodetector. The results show the following: (1) Urban construction land in Nanchang continued expanding from 1990 to 2020, by 385.22 km2, with an average annual expansion intensity of 0.18% and an average annual growth rate of 6.2%. (2) During this time period, the expansion of urban construction land in Nanchang underwent three development stages from: low-strength with low-speed, low-strength with medium-speed, and medium-strength with low-speed expansion. The types of urban construction land expansion were primarily found to be edge expansion and outlying expansion. (3) The overall center of gravity of urban construction land shifts northwest, with significant expansion SW, NW, S, N, and W. (4) Urban planning policy is the dominant driving factor for urban expansion, whereas natural geographic factors have the weakest influence. The results suggest that planning policies should focus on strengthening the rational use and protection of land resources, and promoting the integration and coordinated development of urban functional spaces