基于改进景观扩张指数苏锡常地区城镇扩展空间形态变化

针对目前景观扩张指数计算存在的问题,提出一种改进计算景观扩张指数的方法用于动态分析城镇空间形态变化特征。将景观格局的3 种增长模式:填充式、边缘式和飞地式分别表示为3 种拓扑关系:包含、相交及相离关系,通过判断新增城镇建设用地斑块之间的拓扑关系计算景观格局扩张的各项指数,据此对苏锡常地区1985~2008 年各阶段城镇扩展空间形态变化进行分析。从总体景观扩张模式的变化来看,苏锡常地区建设用地增长方式以边缘式的紧凑增长为主;从增长形态的空间位置来看,各市市区和各镇行政中心的增长形态基本可以归纳为以边缘式增长为主的紧凑增长形态,普通城镇则可能是紧凑增长形态或者蔓延增长形态。计算结果表明,改进的景观扩张指数方法能够动态的反映苏锡常地区城镇用地空间格局形态变化过程。进一步计算反映城镇用地分形特征的盒子维数作对比分析,从计算结果来看,随着时间推移苏锡常地区城镇用地分维数值逐渐增加,从1985 年的1.220 增加到2008 年的1.504,但增长幅度不大,说明城镇空间格局始终处于集中和均衡之间;而景观扩张指数计算结果反映,从1995 年飞地式增长模式的数量和分布开始增加之后,给城镇发展的主导的紧凑模式带来了扰动,这种扩散式的增长导致各城镇扩张的结果在空间形态上出现与总体趋势分异的现象。新建设用地的增长点引起了城镇空间结构的变化,这种发展增加了城镇空间形态的随机性和结构的不稳定性,这个结果可以作为前述盒子维数计算结果的补充,说明景观扩张指数可以解释分形这种形态结果的空间变化过程;并且通过计算景观扩张指数,决策者可以了解城镇扩展空间形态的变化趋势,从而从宏观上控制城镇的无序蔓延。

Urban Spatial Morphology Evolution in Suzhou-Wuxi-Changzhou Region Based on Improved Landscape Expansion Index

Urban spatial morphology evolution can reflect the regional urbanization in the concise and effective way. It comes into effect to achieve the regularity of spatial morphology evolution by identifying landscape change characteristics dynamically with landscape expansion index. In accordance with current problem in landscape expansion index calculation, this article proposes a method that analyzes the characteristics of urban spatial form change by improved calculating landscape expansion index. Firstly, 3 topological relationships (contain, intersect and not-touch) are applied to representing 3 landscape growth pattern which are infill, edge-expansion and outlying accordingly. Secondly, by judging the new patches of urban topological relationship, each landscape expansion index is calculated depending on the definition. And then based on the results of calculation, this article analyzed the morphology of urban spatial pattern evolution in Suzhou-Wuxi-Changzhou (SXC) region in each period during 1985-2008. From the aspect of the total trend of landscape expansion pattern in SXC region, the edge-expansion was the leading expansion trend which was belong to compact growth. Seen from the other aspect, there were differences in the location of the urban morphological growth. In the urban district or the administration center of each town, the morphological growth could be summarized as compact growth in edge-expansion way. And both of the urban sprawl or the compact growth could be found in the rest of the area. The results illustrated that by using the method of the landscape expansion index the morphology of spatial pattern evolution can be analyzed dynamically. Furthermore, box-counting dimension, as one of the most popular fractal methods, was applied to calculating the urban fractal dimension. The results shown that box-counting dimension of the urban in SXC region increased through the years. During 1985 to 2008 the dimension value is range from 1.22 to 1.504 in the low growth rate which means that the spatial morphology of urban was always between the concentration status and the equilibrium status. On the other hand, the results of landscape expansion index showed that patches of outlying pattern increased from 1995 which gave some disturbances to the leading compact growth pattern. This spread pattern caused spatial heterogeneity among the urban and towns. The growth poles of the new construction land brought about the change to the space structure. Urban expansion in outlying pattern would enhance the randomness of spatial morphology and instability to the spatial structure. These results could explain the result of box-counting which fractal method could not explain well. Therefore, landscape expansion index can provide spatial process interpretation for fractal dimension which is the result of spatial morphology as supplementary. Furthermore, the decision maker can comprehend the trend of spatial morphology evolution during the urban expansion by calculating landscape expansion index so that urban sprawl can be controlled by macro policy in the reasonable way.