Exploring the Characteristics and Drivers of Expansion in the Shandong Peninsula Urban Agglomeration Based on Nighttime Light Data

This study takes 16 cities in the Shandong Peninsula urban agglomeration as the research object. Based on the nighttime lighting data from 2000 to 2020, the enhanced vegetation-adjusted nighttime light index is constructed on a five-year time scale using the statistical data comparison method to extract the urban built-up area boundaries, built-up area expansion index, and spatial form characteristics. The following findings have been drawn: First, the urban expansion rate, intensity, and compactness of the cities in the study area are characterized by a year-on-year decline. Jinan and Qingdao show a double-core pattern of urban expansion. In the first stage, the intensity of built-up area expansion is the strongest, and the compactness also shows a decreasing annually trend from the southwest to the northeast. Second, the highest percentage of sprawl is edge expansion with the main urban areas of cities dominated by edge expansion, while counties have a high percentage of outlying. Third, the northern coastal areas of the city's center of gravity and the cities of southern Lunan show varying degrees of divergent trends. The center of gravity of the cities around Jinan is characterized by local concentration, and the mutual attraction of the cities of Weifang and Qingdao is increasing. Fourth, based on the analysis of the center of gravity-GTWR, the main drivers of speed expansion are fiscal and economic, population education, transportation, and urban facilities construction. The compactness expansion drivers are financial, medical, population, transportation, education, and urban construction. The drivers are characterized by a more pronounced spatiotemporal heterogeneity.