Quantitative spatiotemporal evolution of large urban agglomeration expansion based on 1995–2020 nighttime light and spectral data

The spatial distribution of urban agglomerations is an essential component of urban agglomeration development planning. To obtain information regarding the expansion of urban agglomerations over large spatiotemporal scales and long periods, this research quantitatively assess the spatiotemporal evolution of the large urban agglomerations in the Guangdong-Hong Kong-Macao Greater Bay Area (GBA) from 1995 to 2020 based on the multisource nighttime light and various spectral data. The results showed that, from 1995 to 2020, (i) the GBA expanded in a "northwest-southeast" pattern and showed a trend of slow expansion and then rapid expansion; (ii) the longest migration of the centroids of the cities in the GBA occurred in Foshan City (9965.22 m), which migrated at an angle of 37.88°to the west by north; the shortest migration distance of the centroid occurred in Macao (779.65 m), where it migrated at an angle of 33.96°to the south by the east; (iii) the GBA expanded in a "circle radiation" pattern, and the subcentre cities have more significant development potentia; (iv) the distribution of "hot and cold spots" of urban expansion in GBA remained stable; and (v) the aggregated autocorrelation of expansion in the GBA was not statistically significant but underwent continuous "decentralisation". Compared with previous studies, our work rapidly and accurately extracted the spatiotemporal evolution of GBA urban expansion from 1995 to 2020 at a spatial resolution of 30 m, which can effectively supplemented current socioeconomic statistics data lacking geospatial information, and detailedly discussed the geospatial displacements of the geographic elements for all cities to assess the differentiated information and agglomeration effects in the inner areas of large urban agglomeration. The results can provide valuable datasets, vital technical support and decision-making references for constructing sustainable development strategies in GBA and other large-scale urban agglomerations. • Nighttime light and spectral data were used to rapidly assess evolution and clustering effects. • The research area underwent uneven spatial expansion in a northwest-southeast pattern. • Spatial evolution was strong in the easterly direction and concentrated in the core area. • The centroid of cities in the Greater Bay Area evolves in different ways. • Clustering effects of the Greater Bay Area are characterised by decentralisation.