* Latitude had been established in ancient Greece, but the correct measurement of longitude, a function of time, was only made possible in the late eighteenth century, when John Harrison’s chronometer won a fabled competition.

* The man who found it was the German explorer Alexander von Humboldt, who had many other claims to fame in the fields of geography and the emerging science of meteorology. In 1816 he devised the concept of isothermal lines on maps, indicating comparative atmospheric temperatures across the globe.

* There is, almost inevitably in a tale such as this, an intriguing contemporary aside. The Waldseemüller map was lost for hundreds of years, only to be rediscovered in 1901 in Wolfegg Castle in Southern Germany. At the very same castle some decades later Josef Fischer may have forged the Vinland Map.