Measuring the coupling of built-up land intensity and use efficiency: An example of the Yangtze River Delta urban agglomeration

Irrational built-up land expansion debilitates urban sustainability and leads to environmental decay, food security, and climate change. Using the Yangtze River Delta (YRD) urban agglomeration as an example, this research identifies the mismatch between the intensity and use efficiency of built-up land at multiple scales. Specifically, the study gauges built-up land intensity (BUI) using horizontal layout and vertical height data. Land use efficiency (LUE) is calculated by fusing multi-source spatial data, including nighttime light (NTL), land surface temperature (LST), population density (PD), gross domestic product (GDP), and points of interest (POI). The coupling index (CI) between BUI and LUE determines the misallocation of built-up land resources. The results indicate that BUI and LUE match well in YRD, whereas well-coupled built-up land with high BUI and LUE is concentrated in the eastern YRD. Based on the coupling findings, built-up land can be divided into three categories: overloaded, well-coupled, or inefficient. When built-up land is overloaded, it is essential to notice the excessive concentration of urban functions. On the other hand, reducing land resource waste should be a priority where built-up land is inefficient. This research helps confine irrational urban expansion, deploy rational urban expansion plans, and foster sustainable cities and communities.