Abstract: Objective The medial axis(or a topological skeleton)is a thinner version of a geometric object,whichis equidistant from the object’s different edges.It can be seen from this definition that medial axisconstruction involves defining the“different edges”problem.Actually,the graph structure of polygonmedial axis shows that there is a medial axis in polygon convex vertex,and no medial axis(outside thepolygon)in a polygon concave vertex.In this paper,the left and right point method was adopted tojudge if one vertex of a polygon is a concave vertex or not,and then the different boundary segmentsof such polygons were defined and labeled.With the aid of ArcGIS software,this paper presents twomethods for constructing approximate a medial axis for planar free-form shapes:one is vector methodbased on the Voronoi diagram;another is raster method based on the regional distribution based onthe Euclidean distance.Experimental results show that both methods are both effective and feasible.