中文摘要：

不同区域特殊的自然、区位、历史条件，人口、资源、经济发展形成了城镇体系成长的区域背景，在很大程度上，它影响并决定城镇体系的成长过程与发展规律。引入分形（fractal）理论，以兰州-西宁城镇密集区为例，研究西部欠发达地区城镇体系的空间结构、规模结构及其形成机理。通过对城镇体系分形维数的研究，反映特定自然、社会、经济条件下，西部欠发达地区城镇体系空间结构、规模结构特征。城镇体系规模等级分布分散，呈明显的首位分布，大中城市发展不足，城镇体系规模等级总体偏小，人口在城镇之间分布的均匀性差。城镇空间发育度较低，空间分布很不均匀，分散性较强，远离中心城市的城镇密度衰减较快。局部区域的城镇空间发育成熟度差，空间分形特征不明显甚至没有形成分形结构。相比而言，相对发达地区城镇体系规模结构、空间分布呈现均衡化、网络化特征，首位城市发展已经融入到体系的发展中，城镇以群的力量带动区域发展；而欠发达地区城镇之间规模分布、空间分布“齐性”都相对较差，首位城市的“孤岛式”发展决定了区域的发展地位。

英文摘要：

Regional background of urban system growth is formed under the special natural, geo-position and historical conditions, population, natural resources and economic development in different regions, which affects the growth process and development laws of urban systems. In this paper, the fractal theory is used to carry out a case study on the spatial structure, scale structure and formation mechanism of urban systems in the Lanzhou-Xining town compact region, an underdeveloped region in west China. The characteristics of spatial structure and scale structure of the urban systems under the special natural, social and economic conditions in the underdeveloped region in west China are revealed by researching the fractal dimensions of the urban systems. The results show that the distribution of scale grades of the urban systems is dispersive, there is an obvious primate distribution, development of the large and mid-sized cities is insufficient, scale grades of the urban systems are generally low, and the evenness of urban population distribution is poor; the Spatial development degree of cities and towns is low, spatial distribution is quite uneven, decentralization is high, and the density of cities and towns away from the central cities is attenuated rapidly; the mature degree of spatial development of cities and towns is poor in some regions, and the spatial fractal characteristics are unconspicnous and even the fractal structure is not formed yet. Comparatively, the scale structure and spatial distribution of the urban systems in the relatively developed regions are characterized by evenness and network, the development of the primate cities has been in harmony with the development of urban systems, and the regional development is driven by the city-town groups; whereas the integration of scale distribution and spatial distribution of the cities and towns in the underdeveloped regions is relatively poor, and the development of the primate cities in an ＂isolated-island way＂ affects the regional development lev