Robust watermarking of vector digital maps

Digital maps are used, for example, in car navigation systems and web-based map services. As digital data, digital maps are easy to update, duplicate, and distribute. At the same time, illegal duplication and distribution or forgery of the maps is also easy. This paper proposes a digital watermarking algorithm for vector digital maps as a method to counter such abuses of the maps. A watermark bit is embedded by displacing an average of coordinates of a set of vertices that lies in a rectangular area created on a map by adaptively subdividing the map. The watermark is resistant against additive random noise, similarity transformation, and vertex insertion/removal, and, to some extent, cropping.