A Study On The Producing And Topographic Information Characteristics Of 1:250,000 Scale DEMs

1:250,000 scale DEM is one part of 1:250,000 scale National fundamental Geographic Information System database, it is also the important part of building "Digital CHINA" fundamental data frame. 1:250,000 scale DEM can act important roles in topographic analysis of medium size, and it can provide spatial information supports for region planning managing and exploiting of ecological environment national defence constructing disaster monitoring> national macroscopical managing etc. Its elevation information came from the same scale topographic maps. Because of the error of topographic maps and the producing techniques of DEM, especially the impact of generalization of contour lines in map-making and the grid resolution of DEM, there are many terrain representation errors in 1:250000 scale DEM. It is different kinds of error that affect the creditability of analysis and application which based on DEM in different degree.The author chose three test areas : Jiuyuangou in hilK Taibai in Qinling mountain and Guanzhong in plain area. Firstly, the author made a discussion on the production of 1:250000 scale DEMs in different terrain roughness, and produced DEMs of loess hill test area(using elevation point technique) > high mountain test area (constructing topography structure line technique) and plain test area(generating directly technique) based on 1:250,000 scale full element digital maps. Secondly, the author analysed different extractionrmethods of topographic factors N topographic characteristics and water system. Eventually, through comparing the topographic information of basic topographic factors -, topographic characteristics and characteristics of water system with the bigger scale DEMs, the author found that the values of slope, plan curvature ^ profile curvature ^ gully density ^ terrain roughness and the length of ridge and valley and drainage density which all extracted from 1:250,000 scale DEM are all reduced in different degree, however, the values of mean slope length and elevation deviate degree are increased.This research shows that the topography represented by 1:250,000 scale DEM is more flat, the roughness of terrain is more lower, the surface of ground is summarized, the topography is just outlined, so, 1:250,000 scale DEMs can only be used to represent the roughness characteristic of an area in macroscopic scale, but can't be used to analysis topography in microcosmic scale. This research can provide effective helps for user to get the topographic characteristics of 1:250,000 scale DEMs, it can give some reference about accuracy evaluation in applications of medium scale topography analysis, it also can provide basic materials for the research of topographic information spectrum.Postgraduate:Zhao Bangyuan (Geographic Information System)Directed by: Dr. Prof. Tang Guoan...