The problem of how to deal with the three dimensional representation and analysis of terrain surface within the two dimensional GIS, such as GeoStar,is examined in this paper. It is stressed that the concept of visualization is expanded into the whole GIS system. it's much more than visualization,i. e. it enables the data-input more flexible,data interpolation more powerful,model viewing and manipulation capabilities more highly interactive. The author proposes integrating DEM and digital orthographic image with the basic data of 2D GIS to provide 3D realistic environment for geo-referenced multidiscipline applications.