Abstract: An algorithm for watermarking of the vector map is presented. We lay a rectangular grid over the map; according to the classification of density of vertices in each block we modulate the intensity of watermark adaptively, in the tolerance of the coordinates, and a two-value watermark image is embedded repeatedly by displacing the coordinates of vertices. When extracting the watermarks double-threshold combinative detection is used, the proposed algorithm can enhance the intensity of watermarks and ensure the precision and usability of the map. Experimental results show that this algorithm is robust to some processing.

Key words: digital watermarking, vector map, GIS, copyright protection, double-threshold combinative detection