地理环境下的克鲁格曼式城市体系模拟分析

Simulation on Krugman’s Urban System in Geographic Environments

采用层次分析法和模糊集方法,以浙江省为研究区,构造一种能刻画地理影响程度的空间异质性的地理空间,修正克鲁格曼城市体系模型的均质空间假设,以期观察城市体系模型在经济和地理环境下的不同表现。模拟结果显示:1地理环境对模拟城市数目的波动具有持续、稳定的推动效应,但波动幅度不大,说明即使存在外生差异,城市体系演化仍旧主要靠经济系统的内生力量。2在经济或地理环境下,模拟城市的空间分布具有均衡结构,均呈现近乎对称的六边形格局。但纳入地理环境,能明显提高模拟结果与实际结果的吻合程度。3在地理环境下,4种权重模式的模拟结果各不相同。其中模拟城市的空间分布对经济权重占优模式的反应结果与真实环境比较一致,说明经济地理因素对浙江城市体系演化有较大的影响。

To modify the assumed homogenerous space in the urban system model as developed by Kx--ugrnan （1993）, this article uses the fuzzy set theroy, together with the analytic hierarchy process （AHP） approach, and constructs a series of geographic spaces with spatial heterogeneity based on the study case on Zhejiang Prov-ince, aimed at examining the importance of economic or geographic features as determinants of the size, num-ber, and location of cities in this province. The simulation of the Krugman＇ s urban system model shows geo-graphic features indeed play an important role in the simulated broad patterns in the spatial distribution of the Zhejiang＇ s cities, but the urban systems in the study area evolves primarly because of economic geography fea-tures, concisely speaking, the interaction between transport costs and plant-level scale economies. After con-troling for other parameters, this model might predict more cities in this study case when transportation costs are higher, a share of the manufacturing sector is lower, or the elasticity of substituion is higher. Moreover, in equilibrium, the predicted cities can be found to be located according to a spaital distribution of the hexagonal lattice with the realistic economic as well as geographical enviroments. If true geography is incorporated into the model, the assumed space offers better simulating environments, and, as a consequentce, will improve the proformance behavior of the Krugman＇ s urban system model. The simulated patterns of city distribution can be postulated by one variant of central place theory proposed by Water Christaller （1966）. Furthermore, under the surroundings of dispersed scenarios of four weights, an initial advantage in geography over all regions comes into effect leading to a variety of spatial patterns of urban system simulation in this province. Among them, for the Zhejiang urban system as a whole, cities are distributed consistent fully with those observed when these locations have a certain advantage of economic geography over the others. This might suggest that economic geography effects may dominate dynamic process of urban system development over time across space implying that high market potential might be associated with the predicted cities in this study area.