Abstract: A method for extracting features of main roads such as railways and highways from maps, which can quickly calculate the center lines by judging the information of both sides of the roads, is described. It is applied to the automatic computer input of map data and has advantages of passing through the cross points of different kinds of roads correctly, jumping over the bridges, which cut off the roads on maps, automatically without stopping the trace, filling in the gaps and distinguishing the characters between railways and highways effectively. Because there is no neel for preprocessing such as removing noise and thinning, the approach has a higher processing speed. The efficiency of the method is demonstrated by processing binary images of maps with the scale of 1/50 000.