Abstract: A simple and improved algorithm is developed which extracts the polygonal contour representation from a raster format thematic classification map. The design adopts a 2×2 window which is used to scan and extract the boundary pixels of adjacent polygons along each pair of lines of the map. Contours are thus generated as a list of (X, Y) coordinate pairs, together with the attributes of the left and right regions at both sides of the boundary point. In the process of line segment tracking and polygon tracking, various attributes and topological relations are established. The structure, attribute and topological information of the vector data obtained are integrated and standardized, and they are easy to inquire and operate, and make the postprocessing flexible. The algorithm described in this paper has been implemented on a 386 microcomputer.