Based on the work of J.N. de l’Isle, this is a theoretical map of northern Asia and North America, derived from the fictitious accounts of Admiral de Fonte. Published in the supplement to Diderot’s Encyclopédie, it is part of a ten-part series of maps examining the existence of a Northwest passage. Following the de Fonte account, the passage extends across a series of lakes from the Pacific to Baffin Bay. Below it is an equally fictitious Sea of the West, said to be discovered by Juan de Fuca. In the Pacific, voyage tracks of actual explorations by Bering, Chirikov and de Frondat are shown.