上海大都市交通网络分形的时空特征演变研究

分形理论的城市形态发生学研究应用,首先是从交通网络的应用开始的。国内外学者进行的大量案例研究表明,分形分维有可能是表征城市交通网络特征、解释城市交通网络发展,演化的一种较为理想的测度指标。以上海这一国际性大都市的交通网络为研究主体,通过测算上海市不同行政区域交通网络的分维值,研究分形特征的空间变化;利用不同时代上海市全域及典型行政区交通网络的分维,研究分形特征的时间演化。研究结果表明,在上海与一些发展相当成熟的大、中城市与城市化地区,交通网络形态1.7左右的分形分维值具有普适性,有可能是判断网络形态与功能、结构完善度的一个较为合宜的测度指标;分维的变化,表现在空间域上,上海城市交通网络的分形特征内域明显复杂于外域,在城市发展主轴方向表现为由内向外分维测度值的有序降低;而在时间域,近期的交通网络分形复杂度明显高于早期,网络的构型不断得到优化;这一总体趋势,与城市形态开发、经济发展的历程相一致。可以相信,分形测度与分维的演化将成为描述城市形态发生学过程的一个最有用的指标。

Spatial-Temporal Evolution of Fractal Feature in Traffic Network of Shanghai Metropolis

The application of fractal theory in research on the urban morphology is initiated from research on traffic network. A lot of case researches made by scholars at home and abroad have been shown that the fractal feature and fractal dimension would become a relatively ideal and useful measured indicator to remark the form and property of traffic network in a city and explain the process and dynamics of developing and evolving of the network. This paper has taken the traffic network in Shanghai Metropolis as a study case, by using the fractal dimension of the traffic network measured and calculated in Shanghai and its some districts, the spatial changes of the fractal feature have been researched. By comparing the fractal dimension in deferent periods measured and estimated in the city and districts, the temporal evolution of the fractal feature have been investigated. The results show that the value of 1.7 of fractal dimension of a traffic and road network in a lot of metropolises, big and medium size cities and some urbanized areas has a universality’s meaning, it will be an appropriate indicator for evaluating and judging the form, function, structure and perfectiveness of the traffic network. As to the changes of fractal dimension in the spatial field, the fractal feature of the traffic network in the inner city of Shanghai is more complicated than that in the outer city, and the fractal dimension is gradually decreased from the inner to the outer city along the main developing axes of the city. In the temporal field, the fractal feature and complexity of the traffic network in the recent period is higher than that in the earlier, the form strength of the network has been optimized gradually. This general evolving tendency is coincided with the developing processes of the city. It is believed that the fractal dimension and its evolution will become a most useful indicator for describing and explaining the morphological process of the city explicitly together with other useful city’s indicators.