An important map in the sequence of depictions related to one of the most important cartographic debates of the 18th Century. Robert Sayer’s map of the Pacific Northwest of America and Pacific Northeast of Asia was first published in Sayer and Bennett’s The American Atlas, London 1775.  The map is derived from Gerard Müller’s seminal Nouvelle carte des découvertes faites par des vaisseaux russes aux côtes inconnues published in 1754.  Müller’s map, and those published by later cartographers such as Thomas Jefferys and Carrington Bowles, are important to the cartography of the Pacific Northwest region because they helped refute the Buache-Delisle depiction of the coast of the Pacific Northwest published in 1752.  The Buache-Delisle myth was  based on the Russian explorers Bering and Chirikov expeditions to the region as well as on the fraudulent letter attributed to Admiral de Fonte who expounded the existence of a Northwest passage. The controversy in question began when Joseph-Nicolas de l’Isle and his brother in law, Philippe Buache, produced a manuscript map to the Academy Royale in 1750 and was subsequently published with certain modifications by Buache in his landmark map Carte des Nouvelles Découvertes au Nord de la Mer du Sud in 1752, that depicted in an erroneous and speculative manner the  Arctic and Pacific coast with its mythical “Mer de l’Ouest”.
That being said, although Müller is more scientific in his approach in depicting the North American coast, he continues the imaginary leap of speculative faith by depicting the “River of the West” at the “entrance discovered by Martin d’Aguilar in 1609.” This river, through the interior of the continent from the Pacific to Hudson’s Bay, although imaginary, was the basis for many quests in search for the Northwest passage.  Müller also depicts a second entrance to the continent supposedly discovered by Juan de Fuca in 1576 and draws Alaska with its erroneous and elongated peninsula in conformity with the official Russian hypothesis.
These myths and misconceptions on the depiction of the Pacific Northwest and the hoped for Northwest passage would finally be put to rest following the expedition by James Cook in 1778 and confirmed by George Vancouver’s landmark surveys of the North American coast in 1791-95. 
 It is interesting to note Cook’s expeditions along the western coast of America in search of the Northwest passage would in effect be the first time that an English explorer would visit these shores since the claims made to New Albion by Sir Francis Drake in 1578 and depicted on Müller’s map as being located North of California,
(Sources: Kershaw 1112, 1119, 1132, Hayes, D. Historical Atlas of the Pacific Northwest)