Measuring the Urban Sprawl of a Mega-Urban Agglomeration Area Based on Multi-Dimensions with a Mechanical Equilibrium Model: A Case Study of the Yangtze River Delta, China

In the context of rapid urbanization, inefficient, disorderly, and low-density urban sprawl often leads to resource waste and ecological damage. Over the decades, many studies on the measurement, analysis, and governance of urban sprawl have emerged. However, existing approaches lack in-depth research on distinguishing effective expansion from inefficient sprawl. Given the limit of land use resources and the demand for urban development, an accurate and reasonable method for urban sprawl measurement is needed. This study proposes an urban sprawl identification method based on a mechanical equilibrium model to analyze the spatial distribution and spatiotemporal evolution characteristics of inefficient sprawl, using the Yangtze River Delta’s (YRD) urban agglomeration as an example. The study found the following: (1) The inefficient sprawl in the YRD was 5219, 1189, and 980 km 2 in the three five-year periods between 2005 and 2020. (2) From 2005 to 2020, the inefficient sprawl in the YRD was, on the whole, a weakening trend, but Shanghai and Zhoushan showed an accelerating trend of inefficient sprawl. (3) The proposed method is applicable to most urban development patterns and provides implications for urban sprawl control in mega-urban agglomeration areas, such as the YRD.