Study On Techniques Of Urban Land Grading Based On GIS

Land resources are unrenewable resources. With the deepening of China's reform and development, real estate development, and frequentation of land use rights transfer activities, urban land have been scarce resources increasingly. Grading and its dynamic updating of the urban land have also been more and more important.As a Complex process , urban land grading involves numerous evaluative feature, and land grades need regular updating. Merely using artificial rating is inefficient. Manual grading methods with computer's assistance are mostly used currently. These methods require manual intervention, and have stronger subjectivity or low degree of automation.The purpose of this study on techniques of urban land grading based on GIS is to improve land rating automation and scientificalness.Evaluating method with many factors is used in this paper, because it is for computer-assisted land grading .It use vector data structure for grading data and raster data structure for grading unit division. It use GIS spatial analysis to calculate the value of each factor unit and total value of all the factors. It use image classification method to rate the land primarily.The main research focus and innovative results are :1. The paper involves several automatic methods for the rating process, such as, the method of calculating the value of importance of commercial services sites, generating buffer zones for poly-lines, division of site area or overlay of lines and polygons.2. All the methods in this paper are independent of any GIS software. The methods can use both raster and vector data structure , which are basic data structures used by GIS too. So all the methods can be used for any the land grading information systems based on GIS.3. Polygon scan filling algorithm based on boundary marking is designed to rasterize the vector area in this paper. This algorithm can achieve accurate filling of simple polygon, even polygon with "isolated island". It is for the problem of filling related to GIS spatial analysis. This algorithm can fill the sharp polygon accurately. It is better than seed filling algorithm and AET algorithms. This algorithm is widely used for various stages of land rating.All the methods in this paper are tested and measure up《Rules of Urban Land Grading》.These methods can accurately calculate and easy to use in other systems. There are broad prospects for application.