Abstract: Polygonal map overlap is an important technical link in synthetical analysis and evaluation of multi-factor maps. A new method of polygonal map overlap, the method of vector-grid which is fit for being applied in microcomputers, is proposed in this paper. Concerning two kinds of formats:Vector as the main format and grid as the auxiliary format, the method has such advantages as simpler structure, less data, higher efficiency and so on. Because of the complication of the overlap, the reliability of the basic idea of the method is also proved with the theory of complexes from topology in this paper. The method has been implemented in the microcomputer HITACHI MB-16007A, and the initial test shows the system to be feasible.