Abstract: Technique for converting the raster data of polygon maps to vector data is discussed in this paper,based on the analysis and comparison between the raster and vector data formats.According to this technique there may be a boundary point existing between every two neighboring pixels of the raster data,that means each pixel of the raster data has at most eight boundary points with the value of 1 of 0,and the number of boundary points adjacent to another is 2 to 4.Therefore the points on a vector line and their topology can be determined because there is a number of adacent boundary points of 3 to 4 on the nodes of a line.Through surplus point deleting,line smoothing,polygon topology generating,label point creating and feature attribute refilling,the technique can greatly decrease the data amount processed and successfully convert the raster data to vector data.