从图论视角建立区域尺度乡镇公路网络图,并基于节点度D提出等级节点度D_r及规模节点度D_p。从无尺度结构视角,运用D、D_r、D_p指数及数理统计方法描述苏南乡镇公路网的异质结构,结果表明苏南乡镇公路网D并非无尺度结构,但其D_r和D_p符合无尺度结构。利用SPSS相关分析和GIS空间分析发现D_p与D相关性小,但与D_r相关性高且空间对应明显。乡镇D_p-D_r的互动机制空间显示为"核-带"式区域乡镇发展模式,这种开敞组团格局有利于区域发展与保护双赢,由此建议苏州、无锡和常武地区控制乡镇密集分布,集中合并乡镇,适当限制高级公路发展;南京、镇江及金坛、溧阳地区加强高级公路地"带"乡镇的发展力度。

Understood from the viewpoint of Graph Theory, free-scale structure essentially is the exponential function of vertex degree, D, in network graphy. The paper proposes rank vertex degree (D_r) and population size vertex degree (D_p) on the basis of the numeral vertex degree (D) of regional town road networks. Firstly, town road networks are discribed based on mathematics method, which aims to reveal the heterogeneity structure of three kinds of vertex degrees from the math background. The results show that the characteristic of free-scale structure is relative, and changes with the analysis objects and their attribute and scale; vertex degree D does not exhibit free-scale property, while D_r and D_p form free-scale structure; and the exponential function of town poulation sizes of a region corresponds with Rank-Size Rule of urban system. Then, town road networks are analysized on relational analysis of SPSS and spatial analysis of GIS, which aims to find the relationship between town vertex degrees D, D_r and D_p. The results show that the correlation coefficient between D_p and D is 0.569 while the correlationship and spatial contacts on town road networks graphy between D_p and D_r are all very evident. The numbers of roads linked by each town are limited and cannot be changed into free-scale structure because of two-dimensional spatial distribution on earth surface and costly construction expense of these roads. The Poisson distribution of D is affected not only by population size of towns but also town location and others factors. High ranked roads are contact bridges of production and communication among cities whose spatial pattern influences these roads assign and pattern. Accordingly these high ranked roads and "spill-over effect" of urban change road linkage priority mechanism of towns, which results in D_r upgrade of some towns in some specific area. Town population sizes increase with their vertex degree D_r upgrade. D_r and D_p of town road network shows exponential function distributions structure in the end. The above inherently mutual mechanism between town population size and its road linkage rank spatially shows the "Core-Belt" model of town development in the rigion, where the "Core" corresponds to the area around cities, and the "Belt" corresponds to the area around high ranked roads. The open town clusters model benefits both economic development and eco-environmental convocation.Finally the paper suggests that the area of Suzhou city, Wuxi city, Changzhou council area and Wujin city need controlling towns high-dense pattern model, where town centralization and consolidation policies should be conducted, and the development and pattern of high ranked roads need proper control and scientific planning; the area of Nanjing city, Zhenjiang city, Jintan city and Liyang city need to strengthen developing towns around high ranked roads, but avoid the overspread pattern of towns.