Manually digitizing maps for GIS is tedious

time consuming and imprecise. It has been a "bottleneck" in building GIS database. A new algorithm of combining the tracing and topological building to build the topological relationship directly from thinned raster data is proposed in the paper. It makes use of the topological information

that can be easily obtained in the processing of tracing to optimize the algorithm model of topological building

so the efficiency will be greatly improved. Lastly

a new thought of using the connected area fill method to deal with the complex island polygon is also presented in the paper.