The Multidimensional Measurement Method of Urban Sprawl and Its Empirical Analysis in Shanghai Metropolitan Area

Urban sprawl concerns the high-quality and sustainable development of large cities. Due to the ambiguous definition, diversity of measurement indices and complexity of the driving mechanism of urban sprawl, the research results are rich but controversial. How does one carry out multidimensional measurement of urban sprawl? How does one reveal the spatio-temporal evolution characteristics of urban sprawl dynamically? First, according to the three common characteristics of urban sprawl (discontinuity of land use, low population density and inefficiency of land use), we, respectively, measure the urban sprawl of Shanghai metropolitan area by single index and comprehensive indices based on multi-source geospatial data. Next, using geographic information system (GIS) method, the temporal and spatial characteristics of urban sprawl in Shanghai are quantitatively and dynamically analyzed. The results show that (1) land use continuity reveals that fringe expansion is the main mode of urban sprawl, population density exhibits an upwards trend, and land use benefit shows that the sprawl increased first, then decreased and increased again, i.e., "N" type trend. The results of the above three comprehensive superpositions indicate that the urban sprawl in Shanghai changed from severe in 1995 to mild in 2010 and in 2020. (2) From 1990 to 2020, urban sprawl in Shanghai showed a trend of decreasing first, then increasing and decreasing again, which is consistent with an evolutionary trend of newly increased construction land. The larger the sprawl area was, the lower the land use efficiency of the sprawl area was. (3) The main directions of urban sprawl were southeast and southwest, and Songjiang District and Pudong New Area were the main sprawl areas. The peak value of urban sprawl mainly occurred at 20-30 km and was located in the area between the outer ring and the suburban ring. (4) Through time series analysis, we found that the effective supply of housing significantly affected the intensity and scale of urban sprawl but not the speed of urban sprawl in Shanghai metropolitan area. These findings are helpful to reasonably evaluate the real picture of urban sprawl in Shanghai metropolitan areas and provide reference for the formulation of urban sprawl governance policies.