Leon - yes I do know this in considerable detail! I fly as a survey pilot, so my current job entails building topographical maps in remote parts of the world. But even flying low and slow, with large format vertical cameras and the best available civilian IMUs, and then sending out ground surveyors to get GCPs (in order to pin the 3D map to a datum such as WGS84 or DTED, or any of the other standards), we cannot get much better than a metre vertical accuracy. So I would question the accuracy of topo maps in some remote areas of the world if they have only been satellite surveyed and are too hostile/remote to obtain accurate GCP data.