外部规模经济、拥挤效应与城市发展:一个新经济地理学城市模型

External Scale Economy,Congestion Effects and City Development:A City Model of New Economic Geography

新经济地理学城市模型长期忽略了外部规模经济和拥挤效应对城市发展的影响,导致对城市规模和城市空间结构的分析缺少外部性这一重要特征。基于内部规模经济、外部规模经济和拥挤效应的城市发展模型表明,在新经济地理学建模框架下,外部性对城市发展有重要影响。数值模拟发现:福利水平与城市规模之间表现出倒U形关系;最优城市规模随外部规模经济的增加或拥挤效应的减小而不断扩大;人口数量持续增长时,土地租金和总地租收入都以递增的速率增长,单中心空间结构不再稳定,但最终会出现何种形式的空间结构则取决于外部规模经济与拥挤效应的大小。

The external scale economy and congestion effects have been ignored in the city model of New Economic Geography for a long time,so that the crucial feature named externality is absent in the analysis of city size and urban spatial structure.This paper builds up a city development model based on internal scale economy,external scale economy and congestion effects,and analyzes the effects brought by externalities on optimal city size and urban spatial structure.Under the framework of New Economic Geography,our model shows that the externalities have important influence on city development.The numerical simulation shows that there is an inverted-U-shaped relationship between welfare level and city size,and the optimal city size will keep increasing if we enhance the external scale economy or reduce the congestion effects.With a growing population,rent rate and aggregate land rent grow more rapidly,and the monocentric spatial structure is no longer stable,but which style will come into existence is decided by the dimensions of external scale economy and congestion effects.