基于分形理论和Kohonen网络的城镇体系的非线性研究——以长江三角洲地区为例

A NONLINEAR STUDY ON THE URBAN SYSTEM IN YANGTZE DELTA BASED ON THE FRACTAL THEORY AND THE KONHONEN NET

结合长江三角洲地区,探讨分形理论、人工神经网络(Kohonen网络)在城镇体系研究中的应用问题:运用分形理论,计算长江三角洲地区城镇体系规模结构分形分布的分维数和城镇体系空间结构的关联维数,并分析其规模结构和空间结构的分形结构特征;运用Kohonen神经网络模型,对长江三角洲地区的城市进行城市职能分类,分析其职能结构;提出长江三角洲地区城镇体系的发展对策,同时分别评述分形理论和Kohonen网络方法在城镇体系研究中存在的优势与不足,并提出其改进方法。

The paper presents two nonlinear methods, namely the fractal and the Konhonen net, used in the study of the urban system in Yantze delta. Primacy index and the distribution curve of city scale in Yangtze delta are measured. Furthermore, the dimension of the scale structure is worked out to reveal the scale distribution in Yangtze delta. Then, spatial correlation dimension of the townsize distribution in Yangtze delta is also measured to analyses the spatial structure of urban system. In addition, based on the Kohonen net, using the data of the urban work force structure, all cities in Yangtze delta are classified into 5 groups in terms of the comprehensive urban function. According all above analyses it points out three character and deficiencies of the urban system in Yangtze delta, such as: (1) The scale distributing in Yangtze delta is mainly distributed with citysize distributing, partly possessing the characteristics of the first placed distribution; (2) The traffic networks in Yangtze delta does not coordinate with the urban system very much, and the capacity of spatial interaction is a little infirm; (3) Most cities are allaround cities, and the travel function is extremely outstanding in over half cities. But a few middlesmall cities lack the special urban function. Some advice on developing the urban system of Yangtze delta is proposed based on the studying result: The integration of regional should be realized to form regional integration advantage, leading the whole economic development in delta. Such as: (1) Accelerate the step of the internationalization of Shanghai, develop the economy of bigcities, and the integration construction of the three core cities should be further promoted; (2) Perfect the traffic networks and communication networks to strengthen the relation among cities; (3) Realize the effective arrange of the urban function in Yangtze delta; (4) Develop the industry of travel and accelerate the intercity collaboration to build a big tourism circle. At last, the fractal theory was affirmed and the strongpoint of the Kohonen net was presented, namely its unsupervised learning. On the other hand, the improvement method is also put forward.