Keywords北京，城镇用地，扩张度，贡献率，交流强度 Beijing, built-up land, expansion degree, contributing ratio, intercommunicating degree
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Abstract北京作为首都以及全国政治、教育、科学文化中心，其城市化进程在中国具有特殊的参考价值。研究北京地区城市化过程特别是城镇用地扩张及其驱动力，将有利于北京地区经济、社会、生态环境等方面的可持续协调发展，同时也为我国各大城市的生态环境建设、城市化与生态安全的保障提供科学依据。 国内外对于城镇扩张的相关问题研究也随着城市化进程的加快得到越来越多的重视,然而目前有关城镇用地扩张的研究大多局限于单一城镇领域，停留在整体景观水平，缺乏对各地区间相互关系及对不同规模城镇扩张过程的比较分析。因此,本文基于遥感和地理信息系统技术，利用Landsat系列遥感图像的解译成果，对北京不同规模城镇的城市化过程和城镇交流程度对其城镇扩张的影响进行了分析。研究结果表明： （1）近18年来，北京大部分区（县）城镇用地不断向外扩张，迅速侵占、同化周边其他土地利用类型，原有城镇扩张迅速，城镇分布局部集中，范围也不断扩大；其中主要转换为城镇用地的土地利用类型有农业用地、草地、其他用地，而做出最大贡献的土地利用类型为农业用地。它们的转换主要发生在城区范围以及城区周边地区。 （2）各区域城镇规模对其扩张度具有较大的正面影响，且随着城市化的进程其影响程度日益增长。各区县城镇用地的扩张强度是以城区为中心，四周辐射逐渐变慢，且对扩张度起到重要作用的是空间位置和地形条件，也就是说地形条件越趋向于平原，空间位置越接近于市中心，城镇用地扩张机会将越大。 （3）交流环境对北京各区县城镇扩张起到了一定的推动作用，且其作用优势逐渐抵补山区给城镇扩张带来的阻扰。一个区（县）如果他与周围各区（县），特别是与中心城市或离中心城市较近的区（县）有良好的交流环境，它的城镇扩张机会也将越大。
As the capital, Beijing is the political, educational and scientific center of China, and the urbanization of it indicates the especial referenced value to the whole country. The researches of the urbanization process and driving forces of built-up land expansion in Beijing would make for the sustainable development of economics, society and environment of Beijing. Simultaneously the result can also offer some useful experience for the other big cities in China. The related issues have got more attention in the field of urban expansion research as the global urbanization proceeds in recent years. But most of these researches are limited in the single urban unit and are lack of the study of relationship between different towns and urban expanding process of different dimensions. This issue is based on the technology of RS and GIS，and makes an analysis on the influence of intercommunicating intensity and the urban expansion in Beijing, which makes use of the translation result formed by series of Landsat RS figures. The results are showed as follows. In recent 18 years the built-up lands mainly assimilated the surrounding lands, which had resulted in the rapid concentration and sustaining expansion of urban areas at different scales and in different parts of Beijing region. In all land types, farmlands, grasslands and unused lands are the majorities of which transformed to built-up lands, and farmlands take the most percentage of them. The transformation primarily occurs around the region of urban area. Furthermore, the urban scale has positive effect on the expansion degree of built-up lands in Beijing region which was progressively increasing with the process of urbanization. The spatial position and topographical condition also greatly impacted on the expansion degree of urban areas. The nearer the place locates to Beijing city (the urban center), the smoother the urban topography it has, and the more expanding opportunity the urban area will have. Moreover, the intercommunicating environment has had some affirmative effects on the built-up land expansion in Beijing. With the process of urbanization, the influence of intercommunion has recovered the negative effect of mountain regions gradually. Besides, a county’s expansion would get more opportunities if it has been in a good intercommunicating condition with the counties around, especially with the core regions or the counties close to the core regions.