关键词: 交通网络, 城市体系, 地理分形

Abstract: Three types of fractal dimensions were presented to characterize the spatial structure of transport networks. The geographical meanings of these dimensions were illuminated and the methods of the determination of them were illustrated. The three fractal dimensions can be expressed as follows. 1 Length radius dimension: it is always defined by the expression L(r)∝r^D_L where r is radial distance, L(r) is total length of communication lines in the area of π r 2, and D L is the fractal dimension reflecting the change of density of the transport network around a measured center. 2 Dendrite radius dimension: it can be given by the formula N(r)∝r^D_b and N(r) is defined as N(r)=∑rk=1n(k) (r=1,2, …, k=1,2, …,r) where r is gyration radius, k is ordinal number of each ring belt divided with r,n(k) is the amount of branches of communication lines in the k th ring belt, and D_b is the fractal dimension revealing the spatial complexing of transport network. 3 Spatial correlation dimension: it can be expressed in the formula C(r)∝r^D_S where C(r)=1/N²∑Ni∑Njθ(r-d_ij ) is spatial correlation function, θ(x) is Heaviside function (when x≥0, θ(x)=1 ; whereas, when x<0, θ(x)=0), r is yardstick, d_ijis distance between two cities, N is the total amount of cities and towns in a region. When d_ijrepresents‘cow distance’, D_s can be regarded as fractal dimension mirroring the features of spatial connection and configuration of transport network.

Key words: transport network, urban system,geographical fractals