基于圈层建设用地密度分析的中国主要城市扩张的时空特征

基于圈层建设用地密度分析,提出了城市扩张核心度指数;通过计算城市扩张核心度指数和城市扩张强度指数,分析了1990~2010年中国27个主要城市距城市中心不同距离区域的城市扩张的时空模式。研究发现:(1)1990~2010年,大部分城市核心度指数不断降低,城市空间结构变化与国家区域政策密不可分,呈现明显的区域特征。1990~2000年东部沿海地区城市核心度值减少幅度较大,2000~2010年则是东北部和中西部城市降低明显。总体上看,西部和东北部城市的核心度指数要高于东部和中部的城市,结构更加紧凑。(2)城市扩张最活跃的地方总是出现在核心区边界附近,并不断向外推移。(3)城市的形态与城市的发展阶段密切相关。1990~2000年,一线城市扩张的强度和范围远大于其他城市;2000~2010年,二三线城市的扩张强度和范围明显增加。经济比较发达的城市,建设用地的扩张逐渐由单中心扩展向多中心协同发展转变,而经济相对落后西部城市和东北部城市,城市结构比较紧凑,保持着单中心的城市形态。

CHARACTERIZING URBAN EXPANSION OF MAIN METROPOLISES IN CHINA BASED ON BUILT-UP DENSITIES IN CONCENTRIC RINGS

Over the past two decades, metropolises in China witnessed unprecedented growth rates in urban areas. The rapid growth of urban space could lead to a series of problems. The fact that China has the largest population manifests the negative consequences of urban expansion. A rigorous and quantitative comparison of urban growth among metropolitan areas will lend basic support to policy making on regional urban development and will help city planners, economists, environmentalists, etc. This study analyzed the spatiotemporal patterns of urban expansion at different distance from city center in 27 metropolises in China using multi-temporal remotely sensed data. We use three satellite images obtained from the Landsat Thematic Mapper (TM) and Enhanced Thematic Mapper Plus (ETM+) sensor system circa 1990, 2000 and 2010 for each city to develop maps of urban areas. A concentric partitioning method was employed to define urban core area and urban fringe on the basis of built-up density calculated in a series of 1km concentric rings. Urbanization Concentricity Index was proposed to measure the degree to which residential or non-residential development is close to urban core area. Then we calculated and analyzed Urbanization Intensive Index across a series of 1km buffer zones for each city to identify the location-based spatiotemporal patterns of urbanization. UII offers a measure of speed and intensity of urban expansion. The results showed that the spatial structure of these cities was closely related to national policies for regional development, demonstrating obvious regional characteristics. In general, the UCI value of the cities in western and northeastern China is higher in central and eastern China. Most cities exhibited lower UCI value in 2010 compared with 1990, showing a tendency toward dispersion. The highest UII for each city usually occurs around the urban core area and move outward over time. The UII value for second- and third-tier cities became quite small in rings more than 20 km away from city center. The area close to city center witnessed higher UII value in the first decade as compared with the second one. On the contrary, the UII value for the buffer zones away from the city center was much larger in the second decade. Urban form also correlated to the level of economic development to some extent. In the first decade, first-tier cities expanded more intensely and broadly than other cities. Some Second-and third-tier cities experienced significant urban expansion in the second decade, demonstrating a tendency towards decentralization in their development pattern. In 1990, almost all metropolises in China exhibited a trend of comprising one single large central area for the entire landscape. With the expansion of urban land and rapid new nuclei development, some developed cities exhibited a transition of urban space from being mono-centric to multi-nucleated in form, with the emergence of some sub-centers. However, some relatively less developed cities still retained their mono-centric urban space. It can be inferred that urban structure tends to transform from being monocentric to polycentric with the continuous development of economy.