Map Overlay is an important spatial analysis in Geographic Information Systems. This paper presents a novel dual loop algorithm based on R tree to process vector map overlay analysis. The paper first figures out intersection points of line segments with enumerating method of polygon intersection

then uses the matching principle of "import export intersection point" to form the result arcs and further realize the dual loop algorithm of polygon on polygon and line on polygon vector overlay analysis; finally

perfects the algorithm through an efficient spatial access method-R tree index and it's efficient query and filter mechanism to spatial data

so excludes large amounts of unused graphics elements and advances the computational speed very much. This algorithm has been applied to the software development of the commercial geographic information systems. Performance tests confirm that the R tree map overlay algorithm is quick and efficient

and has powerful practical merits.