基于凸壳原理的杭州城市扩展形态演化分析

在城市化快速推进的背景下,探索凸壳原理在城市扩展形态识别中的应用价值,并借此分析杭州市主城区1985~2010年间城市扩展形态演化规律及其机理,以期为控制城市扩展形态,指导未来城市土地开发活动提供借鉴。研究发现,凸壳原理在城市扩展形态识别上简单而明确,通过确定已有城市建设用地的凸壳,将城市所有可开发用地明确区分为凸壳内用地和凸壳外用地2类,为采取差别化的空间管理政策提供依据。构建了基于凸壳原理的城市扩展形态计算机识别方法,有利于在城市扩展模拟中实现城市扩展形态影响因素的定量化表达。1996年之前,杭州市建设用地和凸壳面积增长缓慢,城市形态相对紧凑;1996年之后,建设用地快速增长,城市不均衡扩展加剧,凸壳面积陡增,城市形态紧凑程度下降。总体来看杭州市城市扩展类型属于外延型,随着凸壳面积的增加,城市填充潜力随之增强,为促进杭州市城市紧凑化发展,应该严格控制凸壳外的城市土地开发。沿主干道的城市开发是城市形态外延式发展的主要因素,已有建设用地周边以及城市内部次要道路沿线的城市开发,以及城市中心的集聚作用和规划对城市开发的控制是城市形态填充式发展的主要因素,而郊区化发展和“东扩西进”等城市空间发展政策促使特定时期城市外延式发展。

The Evolution of Urban Expansion Morphology in Hangzhou Based on Principle of Convex Hull

In the background of rapid development of urbanization, this article explored the application value of principle of convex hull used in the recognization of urban expansion morphology, and analysed the evolution and mechanism of urban expansion morphology of main city zone in Hangzhou between 1985 and 2010, with the aim of providing reference for controlling the urban expansion morphology, and guiding the activity of urban development in future. The result shows that, the urban expansion morphology is recognized simply and clearly, using principle of convex hull. It is helpful to provide evidence for making different spatial management policy in different area by dividing the land which can be developed into the land inside and outside the convex hull of urban construction land. The method of recognizing the urban expansion morphology with computer based on principle of convex hull is constructed, which is helpful to quantizing the factors which influence urban expansion morphology in simulation of urban expansion. Before 1996, the construction land and its convex hull in Hangzhou increased slowly, and the urban morphology was compact relatively. After 1996, the construction land increased quickly, and the urban imbalance expansion became remarkable, so the convex hull area increased steeply, and the urban morphology became less compact. In general, the urban expansion morphology of Hangzhou was extension type, and the potential of infilling the urban area increases with the increase of convex hull area. In order to make the urban more compact, the urban development outside the convex hull should be controlled strictly. Urban development along the main road are the main influence factors of urban extension development. Urban development along built-up area and minor road in city, agglomeration of urban center, and restriction of urban development under urban planning is the main influence factors of urban infilling development. Suburbanization and some urban spatial development policy lead to urban extension development in some period.