Abstract: Redundancy point checking is common in data process in Ceographic Information System(GIS), which is very important to improve the quality of geo-spatial data. This paper explored four methods of redundant point checking including their advantages and disadvantages based on a case study of theredundant point checking of digital line graph ( DLG). As such, vertical distance and angle limitationwere chosen as the basic algorithm to check the redundant points in the given data of DLGs in this paper.Then, a visual interactive program for checking redundant points of DLGs was designed and implementedbased on the component provide by ArcEngine. Finally, the performance and effect of the two redundantpoint checking methods in practice were tested and compared with the developed checking tool. The ex-perience results show that, the vertical distance method is better for checking the redundant points ofstraighter line, and the angle limitation method is the better choice for checking the lines with large ben-ding degree and long length. In actual application, it is suggested to select an appropriate redundantpoint checking algorithm based on the characteristics of data and application requirements. 

Key words: digital line graph, redundant point checking: vertical distance: angel limitation, GIS component programming