Abstract: Aiming at the deficiencies of traditional buffer applying to the affected area of the road, a method based on spatial competing is designed to plot net poly. Topological relationship of near regions is established. According to the grade of the road, we use the gravitation model to do spatial analysis and to plot net poly. Then we plot the affected area of the road. Street block from plotted net poly by buffer and by spatial competing are compared. The result shows the method is reasonable.