 He became perhaps better known, though, as a historian and demographer, and certainly so by the public at large.Between 1961 and 2002 he produced a number of historical atlases which, unlike most such atlases, feature fixed base-maps; in most cases, each atlas uses a single principal base-map, which is shown repeatedly, at many dates, as the atlas goes along, thus illustrating changes over the ages, from ancient down to modern, within the chosen area.The accompanying text, typically, is mostly a running commentary on what the maps of a given atlas show.