北京城市蔓延的测度与分析

针对现阶段我国城市用地快速扩张和无序蔓延的现实问题, 以北京市在1996~2004 年期间的城市扩展作为研究案例, 提出可以从城市扩展形态、扩展效率和外部影响等三个方面来判识城市蔓延现象, 并提出基于地理空间指标体系的城市蔓延测度方法, 主要由涉及人口、经济、土地利用、农业、环境和城市生活等方面的13 项指标所组成。实证分析结果表明, 该方法可以有效地测度和量化研究区城市蔓延的特征: ① 建设用地斑块具有明显的破碎化和不规则化趋势, 缺乏良好的规划控制, 不连续开发、条带式开发和跳跃式开发特征明显, 扩展形态不尽合理; ② 新增建设用地的建设密度和容积率较低, 并且新增用地的人口密度和经济产出水平均低于原有用地绩效, 扩展效率不高; ③ 城市蔓延占用大量的耕地和开敞空间、加重了交通负担, 对农业、环境和城市生活存在显著的负面影响。

Measuring Urban Sprawl in Beijing with Geo-spatial Indices

Concerning the rapid urban land growth in recent China, this paper takes the urban growth during 1996 to 2004 of Beijing as a study case, and indicates that urban sprawl can be identified or measured through growth configuration, urban growth efficiency and its impacts of urban growth. It then identifies a geo-spatial indices system for measuring sprawl in Beijing, covering six factors of population, economy, land use, agriculture, environment and urban life quality, a total of 13 indices in all. Specifically speaking, patch area index (AI), patch shape index (SI), discontinuous development index (DDI), strip development index (SDI), leapfrog development index (LDI) and planning consistency index (PCI) are introduced for measuring spatial configuration of urban growth; horizontal density index (HDI), vertical density index (VDI), population density index (PDI) and GDP density index (GDI) are developed for measuring efficiency of urban growth; arable land impact index (AII), open space impact index (OII) and transportation impact index (TII) are used for measuring impacts of urban growth. In order to calculate these 13 indices, different sources data are selected, including land use maps from update survey made by Beijing Bureau of Land Resources, former version of land use master plan, land price and floor-area-ratio samples from land transactions bulletin, digitized map of the transportation lines and county centers, population statistics from the fifth national census and GDP statistical data from Statistical Yearbook, etc. Various GIS spatial analysis methods are used to spatialize theses indices into 100m×100m cells, including overlay, interpolation, neighborhood statistics, distance analysis, etc. Besides, an integrated urban sprawl index is calculated by weight sum of these 13 indices, by which the newly developed land patches are classified into four types: rational development, low-grade sprawl, moderate sprawl and high-grade sprawl. The application result indicates that geo-spatial indices system can capture most typical features and interior differentia of urban sprawl. Construction land in Beijing has kept fast growing with large amount, low efficiency and disordered spatial configuration, which indicates a typical sprawling tendency. The following specific sprawl features are identified by each index. (1) Typical spatial features of sprawling: obvious fragmentation and irregularity of landscape due to unsuccessful enforcement of land use planning; unadvisable pattern of land use growth with typical discontinuous development, strip development and leapfrog development. (2) Low growth efficiency of sprawl: low density of land use growth, low population density and economic output on newly developed area. (3) Other negative impacts on agriculture, environment and city life. According to the integrated sprawl index, sprawling amount in the northern part is larger than that in the southern, but the sprawling extent is in converse case; most sprawling areas include the junctions of near suburbs and outer suburbs, the places along or between highways, etc. Four sprawling patterns are identified: randomly expansion at urban fringe, strip development along highways, scattered development of industrial land, leapfrog of urban residence and industrial area.