Because less data can be hidden on the small vector data set , its copyright is very difficult to obtain protection, and the data is vulnerable to attack, so a new double watermarking algorithm was proposed in this paper. Its main features are: 1) it selected feature points from the sequence of Douglas, then embedded watermarking points on both sides of the feature point, and last embedded watermarking points by wavelet transform again; 2) Further more it increased the map graphic deformation control design. The algorithm was applied to experimental data, and the test results showed that the algorithm had good robustness on graphics, rotation, scaling and shifting geometric transformation of points in graph layers. However, due to the smaller vector data set, so the algorithm is robustness on deletion and cropping of points in graph layers.
