Research On Simulation Of Urban Expansion And Scale Effect Based On ABM

In the current process of rapid development of the urban,there are a series of problems such as the shortage of resources and environmental deterioration,which affects the healthy development of the urban itself and the people's production and life.How to construct the urban growth model scientifically,simulate the spatial and temporal growth of the city reasonablely,to promote the growth of urban wisdom has become the focus of the researchers who are doing researches in the field of geography for a long time.In terms of the extraction of land use rules is not accurate of traditional urban expansion model,the applicability and flexibility of the same model are poor in the scale-oriented transformation,and the forward-looking and foresight is not enough of the urban planning,this thesis takes Chengdu as an example,make a further exploration on three aspects:model construction and optimization,spatial scale effect test and the characteristics of urban expansion and urban form evolution in different situations in the future.The basic data of Chengdu are converted to raster data,each grid is a cell,using the Deep Belief Nets and the Cellular Automata construct the urban expansion model to complete the extraction of the land conversion rules and the simulation of the urban expansion,the Kappa coefficient is used to test the effectiveness of the model.On this basis,the urban quantitative extension Agent is constructed to optimize the urban expansion model.The multi-scheme comparison experiment is carried out to explore the influence of the depth of the network,the balance of the land classification,the spatial scale and the driving factors on the simulation.Based on time sequence,the model is used to simulate the urban form when the land is grow as usual and quantitatively expanded in the next 30 years,the urban form evaluation coefficients such as the fractal dimension,stability index and compactness index and so on are used to evaluate the urban form and complete the urban evolution analysis.The results show that Kappa value reaches 80.82%,and the model has the best result when the network has 5 hidden layers,when the land is classified into 4 classes,the overall Kappa value is the highest,which reached 85.14%.With the urban quantitative expansion Agent simulates the urban expansion,the total Kappa value increased from 80.82%to 81.79%,the Kappa value of the urban land increased from 72.64%to 82.45%,which can overcome the difference between the urban land Kappa value and the non-urban land Kappa value.When reduced the spatial distinguishability,the overall Kappa value will be reduced.When discarded the relative driving factors,the overall Kappa value will be reduced.Under the influence of the existing driving factors,the area of urban land in Chengdu will slow down growth in the next 30 years,and the quantitative simulation of the urban shows that the urban area of Chengdu in 2040 will be 2.11 times of 2010,this expansion process will take up a lot of the original farmland,during the period from 2010 to 2030,the fractal dimension of the urban will gradually decrease,the compactness will increase from 0.0742 to 0.0804,and in the period from 2030 to 2040,the fractal dimension of the urban will increase,the compactness will be reduced from 0.0804 to 0.0697.The research shows that the model can extract the land conversion rules accurately and simulate the expansion of the urban objectively,and use the urban quantitative expansion Agent to simulate the urban expansion can improve the effectiveness of the model.When the spatial scale changed,the accuracy of the model will change obviously,it is necessary to consider the scale as an important factor when constructing the model.In the future,when the scale model is established or the scale model is reduced,the scale change should be considered as a factor.Each driving factor can not be ignored,although the mode of action are different.If the growth rate goes up with the existing growth rate,the urban land of Chengdu from 2010 to 2030 will show fill growth,the border becomes more and more simple,and from 2030 to 2040 the urban expansion will show pioneering growth,and the urban form will evolution from simple to complex.In order to make urban expansion steady and healthy,a compact plan must be carried out to vigorously protect the existing arable land,and control the scale of urban and the speed of urban expansion.