长江中游城市群空间结构的多分形特征

在城市群越来越演化为多尺度、多区域复杂系统背景下,有必要引入多分形理论与方法研究其空间结构。本文基于2018年NPP-VIIRS夜间灯光数据,计算长江中游城市群整体及其局部的多分维谱,根据谱线分析不同尺度下长江中游城市空间结构的多分形特征。结果显示：① 长江中游城市群夜间灯光容量维在整体和局部都出现双标度现象。② q < -5.5时,整体广义关联维谱线突破理论上限2,在q > 0时,武汉城市圈和环长株潭城市群的分维显著较高。③ 整体的局部分维谱和武汉城市圈、环长株潭城市群、环鄱阳湖城市群、宜荆荆城市群局部分维谱表现为单峰偏右。根据上述结果,得到和验证了以下结论：① 长江中游城市群区域一体化程度较低。② 长江中游城市群不同层级和区域的空间结构差异显著,呈现出多尺度复杂特征。③ 长江中游城市群在不同尺度中均倾向于中心集聚式发展。研究揭示多分形模型能够从尺度依赖视角有效揭示巨型城市群空间结构的复杂性及其背后的问题,具有很好的理论探索和实践分析前景。

Multi-fractal characteristics of spatial structure of urban agglomeration in the middle reaches of the Yangtze River

Nowadays, urban agglomerations are increasingly evolving into multi-scale, interregional complex systems. Therefore, it is necessary to apply a multi-fractal method to analyze the global and local properties of an urban agglomeration. Based on the NPP-VIIRS nighttime light data in 2018, this paper calculates the multi-fractal spectrum of urban agglomeration in the middle reaches of the Yangtze River (MRYR) and its four sub-agglomerations, and then analyzes their multi-fractal properties from the perspective of scale. The main results are as follows: (1) The nighttime light capacity dimensions show that there exists a double-scale phenomenon in the whole study region and its four sub-agglomerations. (2) When q < -5.5, the spectral curves of global fractal dimension surpass the upper limit of fractal dimension; when q > 0, the nighttime light fractal dimensions of the Wuhan and Changsha-Zhuzhou-Xiangtan (Chang-Zhu-Tan) sub-agglomerations are obviously higher. (3) The spectral curves of local fractal dimension of three sub-agglomerations of Wuhan, Poyang Lake, Chang-Zhu-Tan and Yichang-Jingzhou-Jingmen show that the peaks of the f (α) curves incline to the right, and the right ends of the curves are higher than the left ends. According to the above results, we can draw some conclusions: (1) The regional integration level of the whole study area was relatively low. (2) There was a differentiated spatial structure in different scales and regions, characterized as multiscale and complex features. (3) The whole urban agglomeration and its four sub-agglomerations tend to develop in a centralized manner. From the perspective of multi-scale interaction, this study proves the multi-fractal model is competent for detecting the complex spatial structure and the underlying problems of mega-urban agglomeration. The multi-fractal model has the potential for further theoretical exploration and practical analysis.