The Study On Cartographic Generalization Based On Topological Relations

The objective entities in geography spatial have a wide range and large quantities. It is impossible to show all of them in the limited map area,then we need proper selection and generalization about the geographic features in cartographic region by the mean of cartographic generalization to reflect the major characters of the geographic features in cartographic region. For example, composition, distribution and connection. The reality is to show the basic and major characters of cartographic region in the limited map area.When the size and shape of map change, although some graphics characters will change, the some characters of graphics will retain. For example, the graphics'adjacency, inclusion, intersection and geometric type (such as points, lines, surfaces) and other characters. These characters that remain unchanged when graphics continuously change are topological characters. The topological relations among the point, line and surface are very complex. The basic topological relations include disjointion relations, adjacency relations, intersection relations, includsion relations. Moreover, these topological relations can be further broken down. Topological relations classification can also take use of the classification model of spatial topological relations based on 4 intersection (or 9 intersection).At present, the study of cartographic generelization more faces one single feature class. In the cartographic generelization process, we only consider the characters of features themselves and the spatial relations among features in the same feature class. This paper selects several commonly used algorithm to achieve cartographic generalization of single feature class about point, line and area. For example, the point features group selection model based on improved convex circle , the point features group selection model based on voronoi diagram, the point features group selection model based on the improved Douglas-Peucker algorithm.When the cartographic generalization process consists of multiple layers, if without considering the topological relations among layers, only making the generalization about a single layer, we will find that the spatial topological relations among the features in the different layers will change, and even bring the wrong topological relations, which affect the accuracy of the results of cartographic generalization. This paper discuss the various topology rules among point, line and area in GIS. For example, points locate lines, points locates polygon boundaries. On this basis of topology rules, this paper discusses the problem of the cartographic generalization based on spatial topological relations among multi-layer, then presents several cartographic generalization approaches based on five kinds of topology rules, and does the related experiments, and achieves the cartographic generalization between points layers and lines layers as well as between points layers and areas layers based on topology relations.