Expanding law and restraining mechanism about urban land:Taking Xi'an city as an example

Economic development that takes evolution of industrial structure and diffusion of po-pulation as the center is the internal motive force of urban land expansion,communication con-nection is the external driving force,and management and planning are intermediate forces.From nationwide point of view,the expanding speed of urban land in Xi'an is lower than the country's average level.The basic reason for the gradual decrease of cultivated land lies in suburbaniza-tion caused by economic development,function substitute caused by adjustment of industrial structure and land adjustment caused by population space division.Based on basic concept and model,this paper points out that equal attention should be paid to"circle expanding model"and"exclave expanding model".The basic elementary theoretical models about urban land expansion include"circle expanding model","leap expanding model"and"radiative expanding model".Under the premise of taping the potentialities,land expansion should regard"circle expanding model"or"exclave expanding model"as equally important in the future quite a long period of time .The former is mainly taken into account in the near future and the latter,at a specified fu-ture date.Finally,factor features(including factor construction,factor transformation,function formation and structural change)and expanding phases about land expansion of Xi'an are identi-fied.