Design And Implement Of Small Geographic Information System

Geographic Information System plays an important role in our society, and many researchers pay more attention to it.How to understand the real world and analysis it by a map view is a great goal even many people have devote themselves to it for centuries. However,it is difficult to develop GIS for that the relation between geography objects is very complicated and the range of GIS is very widely.Several key techniques used in GIS are analysised in this paper,such as spatial data model,expression and store of spatial data, spatial query and so on. The first-line task of GIS is expressing spatial data. Base on vector data model, a whole logical expressive structure of map is designed ,and spatial query and analysis can be builded on it. Spatial topology relation is very important in GIS application. The methods of judging topology relation in points,lines and polygons are analysised in this paper.For computing topology relation between polygons is very complicated, an algorithm of approximating a vector model with grids is put forward in this paper.The method can be applied in some conditions where precition is not very strictly .Based on spatial relation,a set of mature oprerator is designed to analysis and judge spatial relations. At the same time, spatial query can be builded on it.The implement of spatial query relies on two techniques: spatial operator and spatial index.A lots of work of GIS is having access to huge datas in disks. The traditional way of file index is not fit on spatial data. Researching and imeplementing spatial index have become a key task in developing GISAs a dynamic index method,R-Trees is applied very widely in organizing large disk datas.Based on analysising of structure and index mechanism of R-Trees.With thinking of object-orient,a implement method is put forward.Applying the techniques above and refering to experiences of developing GIS, a small GIS platform is designed and implemented. Some types of spatial query,such as point query,intersect query, accurate match query and so on, are implemented in this paper.