Analysis of the space-time transformation of urban structure in Beijing-Tianjin-Hebei using NPP-VIIRS night-time light data

An urban agglomeration represents a mature stage in the development of urban areas with a highly concentrated spatial form. This research paper aimed to comprehend the spatio-temporal evolution characteristics of the Beijing-Tianjin-Hebei urban agglomeration, identify its spatial structure, and interconnections based on the NPP-VIIRS night light remote sensing data from 2012 to 2021. Additionally, the study was supplemented with statistical data from corresponding years to extract the range of urban built-up areas in the study region over the past ten years. The data were analysed using various methods such as light value statistics, urban rank-size rule, standard deviation ellipse, fractal dimension, and measure of urban association. The analysis was conducted based on three aspects: scale, morphology, and spatial structure. The findings indicated that the total amount of light in the Beijing-Tianjin-Hebei urban agglomeration had been increasing steadily, with Baoding showing the highest rate of increase, followed by Langfang. Furthermore, the urban agglomeration had a decreasing trend in fragmentation and fractal dimension, with concentrated built-up areas and regular geometry. The urban centre of gravity was shifting towards the northeast, i.e. closer to the geometric centre of the urban agglomeration. The primacy ratio of the urban agglomerations followed an undulating declining pattern, and the gap between cities in the urban agglomerations gradually narrowed. Although transport integration had led to increased urban connectivity, the northern and southern regions were still not sufficiently connected.