City loop-level Structure based on the theory of division:discussion on the city loop building in Gansu Province

This article discusses the formation mechanism of the city basing on the labor division theory.On this basis,this article establishes the conceptual model of city loop-level quantitative structure by using non-linear programming methods.Then,it constructs city circle structure distribution with Gansu Province for example by analyzing its scale of main cities and the modernization level:capital city as first class central city;resource-based medium-sized cities as second class central city;town-level cities are third class central city;county-level cities as fourth class central city.