First published in 1569, Gerhardus Mercator’s double-hemisphere projection renders the same underlying data used a year later by his friend and peer Abraham Ortelius (Plate 16), with the resulting forms carefully adjusted to accord with the use of a second polar axis. Considered together, these maps indicate a departure from the suggestive and the allegorical, in favor of systematic compilations of hard data, rendered with the maximum accuracy and detail permitted by material and method. The sense of mechanical precision is given further expression in the decorative pattern surrounding the hemispheres, designed to look like brass openwork, complete with rivets and screws.
The aesthetic was characteristic. A craftsman by trade, Mercator’s mastery of metalwork had distinguished him as maker of mathematical and astronomical instruments, as well as an engraver of brass and copper plates used in cartographic work. The motif used here suggests that the map is an essential component of a larger system that includes refined navigational tools, referenced specifically by the illustrations of an armillary sphere above, and a compass below, the needle carefully angled to show the deviation of the magnetic pole from true North. This version, published in 1587, was engraved by Mercator’s son, Rumold, and included in several editions of Mercator’s own atlas.