基于城市年轮模型的城市扩展研究——以沈阳市为例

Research on urban expansion based on urban annual rings:A case study of Shenyang

基于现有城市内部地域结构模型及建设用地扩展模式,提出侧重各方向上建设用地扩展的"城市年轮"模型。构建的"城市年轮"模型由城市重心、扩展方向、年轮单元弧、年轮形态等构成。中国城市扩展过程受五年计划(规划)影响呈现明显的阶段性特征,以沈阳市为研究区,选取1985-2015年七期五年计划(规划)期末年份的Landsat遥感影像,运用"城市年轮"模型,结合城市重心坐标、扩展强度、紧凑度、分形维数对沈阳市建设用地扩展的时空特征、形态特征、扩展模式和机理进行分析。研究结果显示沈阳市建设用地扩展时空分异明显;城市重心整体上向西南方向迁移;城市扩展模式由圈层状转换为沿高速道路放射状、再转换为新城组团式扩展;研究期末城市紧凑度很低,分形维数值很高,表明城市空间形态复杂。自然因素、政策因素、经济因素及交通因素是导致沈阳城市扩展的主要因素。

Based on the existing urban internal regional structure model and the extension model of urban construction land, this paper proposes an ＂Urban Annual Ring＂ model, which places emphasis on analyzing the expansion of construction land in every direction. This model can clearly reflect the growth of urban expansion in all directions, effectively enhance the visualization of urban expansion, and effectively assist us in analyzing the spatio-temporal characteristics and influencing factors of urban expansion. The model of ＂Urban Annual Ring＂ consists of city center, growth direction, annual ring unit arc, and annual ring pattern. Because the urban expansion process in China is influenced by the ＂Five-year Plan＂ and presents a distinct periodical characteristics, this study, taking Shenyang city as the study region, selecting seven Landsat remote sensing images from end years of ＂Five-year Plan＂ from 1985 to 2015, and using the ＂Urban Annual Ring＂ mode, analyzes the space-time characteristics, morphological features, expansion patterns and mechanisms of urban construction land expansion in Shenyang in combination of the urban expansion intensity, barycentric coordinates, compact ratio and fractal dimension. The results show that the spatio-temporal characteristics of the construction land expansion in this region was obviously different. The construction land expansion during the 7th ＂Five-Year Plan＂ period （1986-1990） in Shenyang was slightly higher than the 8th ＂Five-Year Plan＂ period （1991-1995）. Then the urban land continued growing and the expansion intensity gradually enhanced. The city center moved towards the southwest on the whole. During the 7th ＂Five-year Plan＂ period, it moved slightly towards the northeast, and during the eighth, it moved greatly to the southwest. It moved to the northwest during the 9th and 10th ＂Five-year Plan＂ periods （1996-2005）. As the expansion for the 10th ＂Five-Year Plan＂ period （2001-2005） was more balanced in all directions, the range of movement was minimal. By the 1 lth and 12th ＂Five-Year Plan＂ periods （2006-2015）, the city center began to move southwest significantly. The urban expansion mode changed from circle layered to radial along the highway and to the new town cluster type. Till the end of 12th ＂Five- Year Plan＂ period （2011-2015）, the low urban compact ratio and high fractal dimension value indicated that the urban spatial pattern tended to be complicated. Shenyang should optimize the construction land structure, improve the utilization rate of available construction land, and pay attention to connotative development. Finally, the main factors that influenced Shenyang＇s urban expansion were natural condition, politics, economy and traffic.