Gradient Analysis of Urban Construction Land Expansion in the Chongqing Urban Area of China

Urban construction land-use expansion is an important topic in the field of land-use change research. In the present study, the temporal and spatial changes of urban construction land use in the Chongqing urban area are analyzed, based on land-use maps from 1975, 1987, 1995, 2000, and 2010. Using gradient analysis, the study area was divided into nine buffer zones and eight quadrants. The study analyzed the compactness of the urban construction land in different buffer ranges and different directions, and further fitted the compactness degrees and different gradients. The results indicated that there was a rapid growth of urban construction land use in the Chongqing urban area in the period of 2000-2010, and the land use for urban construction sharply increased at an average annual rate of 5.69%. The expansion pattern showed a spatial mode of one center and multiple subcenters. Furthermore, although the key regions (the fastest-growingregions of urban construction land) of urban expansion showed higher compactness degree than the nonkey regions (the slowest-growingregions of urban construction land) of urban expansion, the compactness degrees were decreasing in the key regions but increasing in the nonkey regions. Specifically, the urban construction land had three highly compact zones in the buffer radius gradientzones of radius 5, 25, and 40kmand the compactness degrees gradually increased. When analyzed by the quadrant gradient of buffers, quadrants 45-90 degrees (WNW), 90-135 degrees (WSW), and 315-360 degrees (NNE) were the key regions of urban expansion, and quadrants 225-270 degrees (ESE) and 270-315 degrees (ENE) were the nonkey regions. In addition, the change in compactness degree was highly correlated with changes in the buffer radius and quadrant azimuth. (C) 2014 American Society of Civil Engineers.