以产业结构升级和人口扩散为核心的经济发展是城市用地扩展的内在动力,外部推力是交通联系,中间力量是管理规划。从全国范围考察,西安市城市土地扩展速度不及全国平均水平,其耕地减少的根本原因在于经济发展所导致的郊区化、产业结构演进引起的功能替代和人口空间结构分异产生的用地调整。在城市土地扩展基本理论模式基础上,提出西安市以圈层式和飞地式扩展并重的基本理念,即今后相当时期,城市扩展在挖潜的前提下,应以圈层扩展和飞地式扩张并重,近期以前者为主,远期考虑以后者为主。指出西安市土地扩展的要素特征(包括要素建设、要素转移、功能形成、结构变化)和阶段划分。

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.