Space Expansion Of Large And Medium-sized Cities New Growth Mechanism Research

As the main form of urban spatial expansion, the new urban district, located at urban suburbs, is a new construction area which features the system integrity and functional independence. With the development and construction, the new urban district has been playing an increasingly important role in spatial factors accumulation and pattern reconstructing transition in the past two decades. At the same time, a series of problems are emerging as well. So, it is of great importance to analyze the experiences and lessons, to explore the law and to guide and control the urban spatial expansion. From the perspective of the large and medium-sized urban spatial expansion, a series of models are proposed as follows:the theoretical model of the "anti-wave" for the optimal timing of new urban district establishment, the basic processes of location, the spatial scale forecast formula, the function positioning system and the corresponding regulation mode through analyzing and stimulating the spatial growing of the new urban district and study on mechanism of the new urban district, urban spatial structure adjustment and expansion, the perfection of urban functions, etc.In this paper, the research contents are as follows:(1) The new urban district was established and developed by caused the construction of development zones. Some important factors that affect the development of the new urban district include policy protection, land finance, basic activities, multiple stakeholders and foreign investment. Based on the growth pole theory, the development of the new urban district can be divided into three stages: start-up period, fast growing period, and stable and mature period. In the light of the different driving forces and approaches of the new urban districts, it can be divided into three developing models-reconstructing the development zone, major projects promoting, and integration of villages and towns. At present, the main problems in the development of the new urban district included:the management confusion of government-oriented, the waste of land resources, the pursuit of high-quality and industry-residential separation.(2) The competing models of spatial expansion are established between the new urban district construction and urban redevelopment, which are two spatial expansion patterns. And, the main factors include government action, market mechanisms and the economic development. There is a strong correlation among the optimal timing of new urban district establishment, urban spatial expansion rate and the elastic index of population-urban expansion; however, the correlation between the elastic index of economy-urban expansion is not strong. The "anti-wave" model is revealed when urban spatial expansion rate and the elastic index of population-urban expansion are rising, and rebound times become continuously shortened and intensity strengthened, which shows that it is high time to decrease the pressure by establishing a new urban district.(3) The new urban districts are distributed in the range of11-14Kilometers, and developed on the existing built-up areas. As time goes by, the distance between the new urban districts and mother city are gradually increased. Hence, this paper puts up with the basic processes of location on the basis of scenario analysis that including five stages:background analysis, factor identification, scenario simulation, testing evaluation and strategies defining, which solved the new urban district location problem on the premise of uncertainty for urban special structure.(4) On the basis of the comprehensive evaluation, a conclusion can be drawn that the spatial efficiency is closely related to the government policy, the urban hierarchic, spatial distance, site conditions, and time setting. Moreover, it is tentatively proposed that the threshold of spatial scale is8-20square kilometers, and the maximum upper limit should not exceed the existing urban scale. Furthermore, the spatial scale forecast formula are also put forward based on the land size of mother city and the development potential of the similar new urban districts, which proves that urban planning is one of the main reasons leading to the excessively bigger size of the new urban district.(5) In light of the correlation between the new urban district and mother city and analysis the related background, philosophy, interaction and elements, the function positioning system, called "Region-urban-site", is put forward. The functional configuration of the new urban districts can be understood as solving spillover functions and emerging functions. The processes are as follows:first, to determine the dominant functions; second, to configure the basic functions; last, to select location according to the functions preferences, development possibilities and development connotation.(6) Aiming at the problems in the formation, development and evolution of new urban districts, the corresponding regulation modes are proposed from the following four aspects:management, space, scale and function.