Spatiotemporal dynamics of the urban sprawl in a typical urban agglomeration： a case study on Southern Jiangsu, China （1983-2007）

China has experienced urbanization at an unprecedented rate over the past decades. Against this background, this paper demonstrates the multi-level spatiotemporal urban sprawl process from 1983 to 2007 on the perspective of urban agglomeration with a case study in Southern Jiangsu. Based on a combination of eight rounds of satellite images from 1983 to 2007, the presented results suggest the following three main findings： （1） At the prefecture-city level, the urban sprawl in Southern Jiangsu has presented significantly divergent growth patterns, with more than half of this vast growth occurring in the Suzhou prefecture-level city. （2） At the county level, clear spatial differentiations exist in the direction of the urban sprawl. The centroids of all county seats in the Suzhou and Wuxi prefecture-level cities have an eastward tendency （Shanghai oriented）, while those of the county seats in the Changzhou prefecture-level city tend to be westward （Nanjing oriented）. （3） At the township level, two convergent groups have gradually formed over time; namely, the low density urban zone in the western hilly land and the high density urban zone around the three central downtown areas. The urban areas close to urban cores tend to merge, showing a high-density convergent growth pattern, as do the western and southwestern townships in Southern Jiangsu, showing a low-density convergent growth pattern. All of these findings may be valuable for researchers and local authorities in providing reference for regional coordinated growth, environmental management, and urban planning decision-making.

A new trapezoidal-mesh based data model for spatial operations

This paper presents a new spatial data model based on trapezoidal-mesh for implementing spatial operations within geographical information systems(GIS).Based only on the solid foundation of spatial operations,diversified application models can be established to bridge the gap between Digital Earth models and the real world with its real-world problems(‘connecting through location’).In this paper,the involved polygon features are decomposed into a series of trapezoidalmeshes.Then,geo-processing operations are employed on these meshes rather than the original polygon features,resulting in a relatively simple spatial computation.As a kind of model designed by integrating raster with vector,the model presented here has advantages over other models when carrying out spatial operations insofar as providing a solid foundation for achieving the grand goal of Digital Earth.The concept of this data model and the two extensive examples of its application in spatial operations are elaborated upon in this article.As a result,this article and the research that supports it,proves that the adoption of the trapezoidal-mesh model greatly improves the efficiency of spatial operations in GIS.