以武汉城市圈为例,基于县域尺度,计量揭示了武汉城市圈道路网通达性的空间演化规律:县域通达性演化保持时间惯性,空间分布整体遵循良好的指数律,空间极化程度保持连续,通达性极值的县域分布具有空间惰性;县域通达性基本遵循距离衰减律,呈中心-外围的环状分异,局部出现一定变形,具有强空间集聚性,形成明显的等级圈层结构。县域通达性的这种空间变化受其自然环境"刻画"明显,呈现"反自然梯度"格局,也与其社会经济发展水平密切关联,但不同指标下的社会经济"牵引"强度存在差异,总体上县域通达性与自然-人文地理系统保持空间共轭协同,遵循一定的空间对称性:县域通达性分布遵循中心地原理,与城乡节点体系的靶形分布一致;通达性空间供给与人口和经济需求保持密切耦合,与地形地貌分布具有宏观上的对应性和一致性,空间呈现协同共轭的">"型结构。

Taking Wuhan Metropolitan Area as an example, this paper builds a series of accessibility analysis variables to reveal the spatial-temporal evolutional laws of accessibility of the road network at county level The spatial distribution of road network accessibility, which represented the symmetry establishing or breaking of Natural-Human Geography, is actually resulted from the "carving" of Natural Geographical pattern and the driving of the distribution of Economic Geography, it's also the spatial response of synergistic effect between self-organization and hetero-organization of Natural-Human Geography System, showing the unity of opposites on proportionality-centralization, stability-dynamic, deterministic-randomness, symmetry establishing-breaking. Therefore, this paper interprets the spatial symmetry principle of the county accessibility of Wuhan Metropolitan Area based on the action mechanism of Natural-Human Systems. Generally speaking,although the boundary contour and surface morphology of Wuhan Metropolitan Area is an irregular body,some kind of symmetry order under the action of the man-land relationship is hidden behind that, this order not only showed the symmetry of node location distribution, also showed the symmetry of node intrinsic attributes.