| Studying the phenomenon of urbanization, analyzing the change and extension rules of urban structure and building models to simulate the process of urbanization is very important to direct the urban land scientific and effective planning and using. Among many models, the one based on the theory of Multi-Agents System (MAS) is focused because of its specialty that it can reflect the base evolvement rule "from bottom to top and from micro to macro" of the complicated system fully. Based on the micro-economics and land-use niche theory, paper takes the phenomenon of China cities' residential land growth which occupy a significant proportion of the expansion of urban space in the past 10 years as the studying role, then uses GIS technology and modeling method of MAS, in the end builds a urban residential space expansion model based on the set scenes. Two districts of Hongshan and Wuchang in Wuhan city are chosen as study districts to prove the effectiveness of the model. By comparing the outcomes of the model, paper analyzed and evaluated the benefits of land resources of the residential land resources development in different scenes. In order to build and rectify the model, paper works as follows.1. The research on theory basis and realization mechanism of the model(1) The research on the driving force mechanism of urban expansion is the basement of urban expansion modeling studies. The competitions of the survival space of every urban functional activities are the one of the land resources, in fact which are very similar with the competitions among the different biological biomes for foods and survival space. So many overseas and internal researches introduce the biological niche theory which is usually used to explain the biological competition behaviors to make clear the change rules in the urban land using system, and concludes that the contrast among the different land use types'niches are just the driving forces. At the same time, from the aspect of the relationship between "land use agent" and "land use object", the contract of land use niches are measured by the value of the marginal utility of different land use type, then how to weigh the value of the marginal utility is decided by the degree of land use agents'recognition of land use utility. Based on this point, the paper puts forward an academic model of the urban residential land niche breadth extension.(2) The extension of the urban residential space is just the interaction processes between the residential land resources niche agents and the residential land requesting niche agents. The residential land resources niche agents afford the resources conditions which are needed for the extension of residential land, while the natural and social resources are asymmetric in the whole urban space, there is a residential land resources niche field which is the prerequisite that residential location differences can come into being and at the same time the bases of the urban residents'behavior of selecting the favourite residential locations. Next, paper defines their roles of the three intelligent residential land requesting niche agents—urban residents, land agent and urban government respectively from the microeconomics point, analyzes their forces and influences on the extension process of urban residential space and summarizes their behavior characteristics function in the end. Especially from the concept of maximizing consumer utilities and by integrating GIS technology and the characteristic of the natural and social resources'asymmetric distribution in urban space, paper analyzes an urban family's utility components and modifies the typical Alonso model by considering cost of time distance as a core. In the end gets a utility model which is used to describe the utility when urban residents searching the ideal residential location.(3)In the paper, such a point is considered that the motive of building an urban growing model is not getting a copy of the real urban growing situation entirely, but extracting the pivotal factors and common laws of urban growing because of the complexity of the urban itself and the instability of human society and economic activities. So different from the researches ago, the paper uses the method of scenario analysis to extract the pivotal factors which influence the process of urban growth, based on the analysis of these factors'instability, the paper builds some scenarios about the urban residential space extending situation as the micro backgrounds of the urban residential growing multi-agents model.(4) The paper builds an experimental environment of the model is by VC Studio and GIS/RS software platforms. In the model the computation and records of every ecological niche factors and the realization of the function of urban residents'behavior of choosing the ideal residential locations are mainly considered. Different from the former researches, the model adds the consideration of the commuter time cost and simulating the urban resident agents'behavior of selecting the favourite residential locations more realistically. A reasonable multi-agent model should follow the modeling mechanism of "from bottom to top", namely must consider the engagements between the microscopic aspects of the problem and the macroscopic ones fully. In the realization of the model, paper sets some macroscopic variables such as the number of urban residents agents, macro economic anticipated, urban government's land policies, and so on which can be adjusted in different model scene, so paper can fully consider the multiplicity of scenes to control the model movement process.2 model demonstration analysis and main conclusionsTaking the Hongshan district and the Wuchang district in Wuhan city as the experimental objects, paper simulates the expansion condition of their residential space in the time span from 1998 to 2008 in order to verify the validity of the model. Then according to "Wuhan 2006-2020 Year City Overall Planning", paper forecasts the residential space growing situation after 2008 based on the prescriptive scene, at the same time carries on the appraisal of the outcome of the model on various scenes.Some main conclusions are given as follows from the model's outputs, (1) In the past ten years, residential space evolution of the researched districts takes the old city transformation and the suburb expansion as the chief features, both are the results of action brought about by land economical ecology niche differences. (2) As compared with the model's simulating result under the different scene condition, there are always intersection between the reality residential space evolution and the model's simulating resulte of different scene which means that because of the influence of macroscopic environment, urban government may adjust its land use policy, natural environment protection policy and so on in different periods, this is just one of characteristics of Chinese real estate market. (3) From the model simulating results, urban residents have regarded the rights and interests of themselves more and more, at the same time because of the action of market economy mechanism the real estate developer also pay more attention to the favorite choices of urban residents; and the urban government also take more attention on the public willing and the growth of resident welfare. (4) As showing in the results of the model from different macroscopic parameters, to regulate the urban population rising rate, particularly the population mechanical rising rate is a key factor to control urban residential space's extending speed; From the results of adjusting the correlative factors when urban resident agents choosing the favorite residential locations, the adjustments of the factors of land base price layers(house price) and cost of time distance have the most influences on the model simulating results, which means house price and traffic convenience are the main factors urban residents concerned about, this also reflects from another side, in the consumer community, the mid and low income crowd still hold comparatively proportion.3. Main research innovation and limitationPaper's main innovation and the contribution includes:(1) from the internal causes and driving forces of urban residential space's extending, the paper analyzes every type of microscopic and intelligent agent's behavior character and interaction each other, and uses related microeconomic concepts and methods to define various agents'behavior character. (2) Considering of the spatial distribution differentiation character of nature and social resources in urban regions, the paper puts forward the concept of urban residential land ecology niche field, while the urban residents'processes of choosing the ideal residential locations are really the processes of choosing the proper residential locations which should match to "the ecology price" of themselves in the urban residential land ecology niche field. (3)The paper improves the classical Alonso model, and builds a new model that can measure the utility which urban residents can get when choosing the ideal residential locations more factually and more roundly. (4) By introducing the scenario analysis method, paper extracts and analyzes the pivotal factors which influence the growing process of urban resident space possibly, then put forwards different scenes, and realizes variable corresponding scene by adjusting the factors and carries on the analysis appraisal to different results.Because of lack of sufficient economic theory and knowledge, the analysis to some economic problems of urban residential space's successive extending processes are still insufficient. Otherwise there are close interactions among the commercial land's evolution, industrial land's evolution and residential land's evolution, because of the limited research capacity and energy, the paper only consider the residential market but other relatively markets are ignored. In brief, the paper still have huge research space left, the model is also on the attempted research stage, the overall frame and the technical route waits for the further revision consummation.
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