京津冀城市生长和形态的径向维数分析

Radial dimension analysis of growth and form of cities in the Beijing-Tianjin-Hebei region

城市生长与形态是地理学规模与形状研究的重要内容,分维则是刻画城市形态、反映城市生长的标度指数。论文以城市建设用地为研究对象,采用2000、2005、2010年3个年份的遥感数据,利用分形理论的径向维数和相应的标度区概念分析京津冀城市和城镇体系的空间格局及其演变特征。结果表明:其一,北京市第一标度区的范围最大,10 a间增长幅度也最大,对周边城市产生阴影效应;其二,以北京为中心,距离越远,第一标度区范围有越小的趋势;其三,几乎所有研究区内城市的第一标度区空间都被建设用地过度填充,外围则各有特色;其四,经济水平对京津冀整体城市建设用地扩张的影响最大,但北京的城市建设用地扩张已经由经济因素主导转变为人口因素主导;其五,随时间推移,第一标度区拟合径向维数效果提高,第二标度区拟合效果降低。由此得出结论:(1)北京在京津冀体现了城市首位效应和阴影效应的双重效应。一方面,京津冀地区城镇化区域体现出了以北京为核心的中央集聚特征,另一方面,北京市的巨大吸引力抑制了毗邻城市的生长。(2)城市中心和外围都出现二元化格局。地区内各个城市的中心部分过于紧凑,而外围则相对凌乱,中心-边缘缺乏一体化过程。(3)人口可能成为未来京津冀城市发展的第一动力。人口集聚的规模效应未来可能替代经济报酬递增效应。这些结果和结论有助于学术界和管理部门从新的角度认识京津冀城市化现状和未来的发展趋势,以便制定更为合理的城市发展政策和方针。

Urban growth and form are important contents of geographic research on sizes and shapes.Fractal dimension is an effective scaling parameter to describe urban form and reflect urban growth.Based on remote sensing data of construction land in 2000,2005 and 2010,this study analyzed the spatial pattern and change of cities and towns in the Beijing-Tianjin-Hebei region.Fractal measures,including radial dimension and the corresponding concept of scaling range,were applied.The main results are as follows:1) The first scaling area and its growth rate of Beijing are the largest in the Beijing-Tianjin-Hebei urban system,producing a shadow effect on the surrounding cities.2) On the whole,the farther from Beijing,the smaller the scope of the first scaling range of other cities.3) For almost all the cities in the Beijing-Tianjin-Hebei region,the first scaling areas are overfilled by construction land.4) Economic development level has the greatest impact on the overall urban construction land expansion in the region,but the driver of urban construction land expansion in Beijing has changed from economic factors to population factors.Based on these findings,several conclusions can be drawn:1) Beijing has dual effects in the process of urban development in the region,including the primary city effect,and the shadow effect.While Beijing drives the development of the Beijing-Tianjin-Hebei region,it also inhibits the growth of some other cities.2) The central part of each city in the study region is too compact,but the development of the peripheries is relatively disorderly,and the main city areas and outskirts lack integration.3) Population may become the key dynamics of the urban change in the Beijing-Tianjin-Hebei region.The principal role of economic return growth may be replaced by the economies of scale based on urban population agglomeration in the future.These results and conclusions may help the research community and government authorities understand the status quo and future development trend of urbanization in the Beijing-Tianjin-Hebei region from a new perspective.