What a strange concoction this late-18th-century French map is. Centred on the northwestern part of America, it is an eclectic mix of geographic fact and fiction. Some continental contours are instantly recognisable, for instance the Kamchatka peninsula of Russia’s Far East, and Canada’s Baffin and Hudson Bays. But what is that thing in between, and what has it done to Alaska?

Even the mapmaker must have known there was something wrong with what he wrought. Notice the contrast between the mostly soft-edged shores of this half-baked Alaska [1], and the jagged coastlines of the real parts of the world. The lack of detail for the former is intentional, a sign of deference by the cartographer to his lack of knowledge. Smooth shorelines are a code between the maker and reader of maps, to be read as: Not yet surveyed.

Then take a look at the larger shape of this alternate Alaska, to the islands populating its northern shores, and to that strange strait that connects Pacific to Atlantic, while skirting both aforementioned Canadian Bays. They’re proof of a curious constant in mapping fake geographies: even though imaginary islands, rivers and coastlines are as random as real ones, they mostly look like the fantasies they are. There’s just something inimitable about the haphazard quality of truly natural geography.

This map appeared in the third volume of Diderot’s Encyclopédie as Didier Robert de Vaugondy’s version, dated 1772, of an English map by Thomas Jefferys (1768). It purports to be a General Map of the Discoveries of Admiral de Fonte, representing the great probability of a North-West Passage.  

This was a popular map, as the Northwest Passage was a popular fantasy - and a prime example of wishful mapping. The Passage found its origins in the early days after discovery, when America was still seen by Europeans as an obstacle to trade with China and Japan, rather than as an opportunity in its own right. Its existence was first mooted in 1539 by Francisco de Ulloa, whose voyage up the Gulf of California [2] led him to propose that it was one end of a strait that ran all the way across the North American continent to the St. Lawrence River, flowing from the Great Lakes through Québec into the Atlantic.

This waterway, all the more mythical for being non-existent, started showing up on maps from the mid-16th century onward as the Strait of Anian, probably after a Chinese province mentioned in Marco Polo’s Travels [3]. For centuries, it was one of that handful of fictional drivers of real exploration. Others include the Seven Cities of Gold (in North America) and El Dorado (generally sought in South America). These places were always sought after but never found, and thus instrumental in pushing back the boundaries of the unknown.