Abstract: The MQUAD algorithm is an efficient watermarking algorithm for vector digital mapping, however several problems were found from our investigation. A double embedded robust watermark scheme for vector digital mapping is then presented,as an extension to the MQUAD algorithm.The vector map is subdivided into two layers by the character of objects in the map.A watermark bit is embedded by two different methods in two layers of the same map.After the displacements of a set of vertices are computed,the vertices with their displacements shorter than thresholds are selected,and an average of the displacements,or the watermark bit is obtained.Experiments show that the watermarks are resilient to additive random noise,local deformation and several cropping.