The Cartographer is an item added by the OpenBlocks mod.
The Cartographer is used to create 3 dimensional maps of the world surrounding the player. Sneaking while right-clicking the Cartographer with an Empty Map will start the mapping process. It will follow the player while recording the surrounding topography. Sneaking while right-clicking the Cartographer again will give you a Height Map, which you can place in a Height Map Projector to create a 3d map of the topography the Cartographer mapped.