The Bodleian’s Map Room Blog (no relation) has a post about the “unsung heroes” of mapmaking: the engravers.
Until the nineteenth century, virtually all printed maps were produced by engraving the map on a sheet of copper—or later on, steel—as a mirror image of how the finished map would look. The plate was then inked and the image printed onto a sheet of paper in a printing press. This was incredibly skilled work, but often only very discreetly acknowledged, the engraver’s name appearing in tiny, modest letters in the bottom margin.
Identifying the engravers for cataloguing purposes—something a library like the Bodleian tries to do—can be a challenge.