The Study On Suitability With Different Evaluation Units For Construction Land In Mountainous Villages

At present,our country is strengthening policy support to the western region gradually,with strengthening the development of mountain region in the west, and the demand for construction land is increasing.At the present stage,our country urban agglomeration scope expanding gradually and urbanization is being pushed further,rural area also gradually follow the way to development of city, which planning at first, followed by construction.In the process of urbanization,the reasonable planning of original urban and rural areas, is the premise to realize scientific development, and it required to make a comprehensive and rational evaluation for the constructional suitability of the land, which will be constructed.In the existed evaluations of construction land,most of them are about plain region and city,the evaluation theory and method have been relatively mature. But the number of evaluations about villages and small towns in mountain area is few,the methods and theories mostly referenced the study process of plain region and city,with some critical problems.For example,the selection of evaluation unit,the construction of index system and grading of evaluation factors,etc,and most popular of them is the selection of evaluation unit.The most commonly evaluation unit is grid cell,in the plain area,as most evaluation factors relatively simple,such as landform and social form,the variation of classification about evaluation factors in different size grid cell is small.But in the mountainous region,as part of evaluation factors complicated,such as geography environment and human condition,the variation of classification about evaluation factors in different size grid cell is wide.On the basis of the existed evaluations of suitability for construction land,this paper integrating with the task of "twelfth five-year" national science and technology support plan”Town regional spatial planning and land use optimization technology integration demonstration "(Project Number:2012BAJ22B06),entitled " The Study on Suitability with different evaluation units for Construction Land in Mountainous Villages ". It will majorly study the changing of evaluation results about construction land suitability under different evaluation units in Mountainous Villages.Through the analysis of the commonly used evaluation units,this paper ultimately determine “the influence of grid cell size on the evaluation result of suitability for construction land " and " the application of mixed unit " two study points.The grid unit set up a basic group and four reference groups,and the mixed unit is first proposed in evaluation of suitability for construction land with introducing slope unit from the geological disaster risk zoning.The whole process is in the case of Shilong in Banan District of Chongqing,combined with the specific situation of Shilong,and constructs a evaluation index system about five layers,that are ecological safety,geographic and geomorphic conditions,geological conditions,natural disasters and socioeconomic conditions,totally 21 evaluation factors.Then using weighted superposition method of the comprehensive index method as the evaluation model,and relying on Arc GIS technique to make classification for each evaluation factor,finally obtaining the final evaluation results of suitability.Through the analysis of the evaluation results,it can be known the influence of grid units size on the classification of geographic and geomorphic conditions is large,and the other fours are little. The greater the grid cell is,the worse of the suitability for slope position and surface curvature will be,and the suitability for slope gradient will be better,but the classification results of relative elevation and slope direction are almost invariant. And the analysis results show that,the evaluation result of the basic group of grid cell(30 x 30 square meters) accords with the specific situation of Shilong town in Banan District preferably.Comparing the results of mixed unit and grid cell(30 x 30 square meters),it shows that under mixed unit the suitability for slope direction is better,for surface curvature is worse and for slope gradient is concentrating in the middle area,and the final result of classification is overall better.