Known as the Sundial Map, this ingenious projection by the German mathematician Franz Ritter represents a masterful integration between cartography and astronomy. Knowing that a properly constructed sundial demands a precise arrangement of parts unique to the place where it’s going to work, Ritter developed this map to function as part of a dial built specifically for Nuremburg. With a gnomon at the North Pole aligned with the central meridian and with the Tropic of Capricorn drawn to follow the shadow this gnomon would cast at Nuremberg’s latitude, Ritter established the basis for the rest of the projection. Plotted to conform with the varying degrees of distortion in each part of the grid, his landmasses maintain correct scale at each point.
This calculated integration of a map and a sundial underscores the mathematically unique relationship that each point on the Earth has to the Sun, Moon, and stars. By creating a map that works in one place only—and with only one correct orientation—Ritter demonstrated the extent to which astronomy and cartography could be aligned by using the geometry common to both. As the same time, he underscored the extraordinary challenge involved with the production of reliable, large-scale cartography. For a map to be trustworthy, it must be astronomically accurate at each and every point. Since the quality of the underlying observations cannot be seen directly, faith in maps needed to be built through a long series of revisions that could be seen as stabilizing over time.