Although multi-municipal cooperation is promoted in Japan, it is affected by the geography of adjacent municipalities. Therefore, the purpose of this article is to analyze what affects adjacent municipalities that arises in a triangulating planar graph and to grasp the progress of the multi-municipal cooperation projects in Japan. We derive the rate of edges and facets crossing borders by use of Euler's polyhedron theorem in a planar graph. In addition, we examine how prefectural borders inhibit the multi-municipal cooperation projects of regional revitalization grant.
