基于分形理论的新疆干旱区绿洲城镇体系研究

Oasis urban system in arid area of Xinjiang based on fractal theory

城镇体系具有自分形性。运用分形理论,对新疆干旱区绿洲城镇体系等级规模与空间结构进行了分析,验证了新疆绿洲城镇体系的规模分布和空间布局均符合分形的特征,得出以下结论:第一,新疆绿洲城镇体系的分形结构在空间上是从核心城市向边缘地区扩散发育的分形结构;第二,新疆绿洲城镇体系空间城镇分布情况只在局部空间存在分形,空间结构虚有框架但缺乏内部联动,整体结构不佳;第三,新疆绿洲城镇体系等级结构较为松散,首位度过高,人口金字塔呈"倒三角"结构,城镇体系发育不成熟,交通可达性对分形具有缓冲的效果;最后在上述分析的基础上,结合近来主体功能区思想,对城镇体系结构优化提出建议。

Measurement is the basic link between mathematics and empirical research,however,urban systems as fractals cannot be characterized with common measures such length,area,density,etc,the fractal dimension is of significance for the studies on urban form and structure.The paper demonstrates that the spatial structure of urban systems can be characterized with multifractal,and moreover,cities index（S 2,S 4 and S 11） also can be used to analyse the multifractal structure of urban systems,which may be implies the course of events as sort of phasetransition from a rural to urban settlement system during the course of regional urbanization.Based on fractal theory,the paper takes the Xinjiang arid region oasis town system as an example,and studies its grading scale and spatial structure.The results show that fractal dimension quantitatively describes the Xinjiang arid region oasis town system exactly,and the major Xinjiang arid region oasis town system take on self-similarity,validation of the size of the distribution system and space layout of the Xinjiang oasis town are in line with the fractal characteristics.Firstly,the Xinjiang oasis town of fractal structures in space is from the core city region to edge of the spread and development of fractal structure;Secondly,the Xinjiang oasis town of urban space distribution exists only in the local fractal,the spatial structure of urban system is regionally and locally discordant,the framework of a virtual lack of internal linkage,the overall structure of poor,the capacity of spatial interaction is weak;Thirdly,the Xinjiang oasis of urban system is more loose hierarchical structure,the size-scale structure is loose;the law of the primate town is too big but just single one;the middle town is absent,and the mostly small towns lie on a geographic elements which are Tarim River,Tianshan Mountains,Longhai Railway and Ili Riverside;which are so overall that the first distribution obviously,the population pyramid was ＂inverted triangle＂ structure,urban system is immature.In addition,the spatial relating degree and spatial interaction among cities are generally slow and sparse in Xinjiang,the non-balance of regional urban network waits for the enhancement,a certain extent,the traffic accessibility could buffer the fractal effect;Finally,the paper discussed the causes of the urban system＇s fractal features,basis of the analysis and the thinking of Major Function Oriented Zonings,which could be helpful for improving the urban system by means of fractal theory and provide the urban system structural optimization and make a reasonable cities development policy and the plan in Xinjiang.