Analysis of city spatial expansion characteristics and influencing factors of transitional zone city:taking Zhangjiakou city as an example

The main factors of the transition zone of city spatial expansion are various in different historical periods. The evolution of Zhangjiakou city development was discussed with the Zhangjiakou as an example which is in the ecotone between agriculture and animal husbandry,using the remote sensing image data,historical data and spatial analysis methods geographic information system,the characteristics of the city spatial expansion was determined,and the main factors which affect the city spatial expansion were put forward. The results show that,Zhangjiakou city′s growth pole has migrated from up fort-down fort-north train station-south train station; city area has expanded 5 times from 1975 to 2013,especially in the fastest expansion rate since 2004;and the spatial expansion direction was mainly to the south;the city space set in the 700-800 meters elevation by the early development to the city surrounding uplands changing to the ocean valley south since 2004. The regional difference between transition zones on both sides of the inherent produce the different way using space to benefit,which is the fundamental driving force for city spatial expansion. In the period of instability,the special terrain condition of transition zone met the need of the first city of military defense domain,gave birth to the city ground; the different climatic conditions and the different production and life modes it generates produced the demand of commodity exchange in the farming area and pastoral area,accelerated the city development;the transport improvement accelerated the agglomeration and diffusion of production factor; the policy financing or not become the political foundation of population distribution,which affects the rise and decline of the city. The transition zone city media functions of circulation will be highlighted for ecological elements,and become the key factor influence city space in the future.