Vector Map Overlay Algorithm Based on Improved Quadtree Indexing

Map overlay is an important spatial analysis in geographic information systems（GIS）. First‚it finds out intersection points of line segments‚then uses the matching principle of “import-export intersection point” to form the result arcs and further realizes the dua-l loop algorithm of polygonon-polygon and line-on-polygon overlay analysis.The original quad-tree indexing structure is improved to handle space split and node assignment‚resulting in enhancing the computation speed.This algorithm has been applied to the software development of commercial geographic information systems.