This important map depicting the discoveries of James Cook’s famous Third Voyage to the Pacific North West of America in search of the Northwest passage in 1778, was published in the Atlas that accompanied A Voyage to the Pacific Ocean, London, 1784.  As such, it is the official version of Cook’s famous expedition that was published  in contrast to Lt. Henry Roberts’ more precise but controversial Chart of the N.W. Coast of America and the N.E. Coast of Asia Explored in the Years 1778 and 1779. Prepared by Lieut. Heny. Roberts under the immediate Inspection of Capt Cook . . . 1784, more commonly known as the "Legendary Lost Chart of Captain James Cook”.
The fundamental difference with the “Loss Chart” is Roberts’ depiction of the Arctic discoveries of Samuel Hearne, a full decade before his journal and maps were to be published.  Hearne, a fur trader for the Hudson’s Bay Company, is known as the first European to reach the Arctic Ocean by an overland route via the Coppermine River in Northern Canada.  As such, Roberts’ chart is the first to publish, what had until then been only drawn in manuscript form by  Hearne, of the impossibility of a Northwest passage through Hudson’s Bay.  Furthermore, Roberts’ chart depicts, in much greater detail, the interior of the North where traders for the Hudson’s Bay Company  plied their trade.
The question as to why Roberts’ chart may have been dismissed from the official account could be a result of the involvement of Alexander Dalrymple in the selection process.  On one hand, Dalrymple may have harboured ill feelings towards Cook for having been chosen, instead of him, to lead the Second Pacific Voyage in 1772-75 that ultimately disproved the myth, propounded by the likes of Dalrymple himself, of Terra Australis Incognita. As such, Dalrymple may have wanted to downplay Cook’s achievements and discoveries.  Secondly, it could be argued that the Hudson’s Bay Company may have willfully tried to suppress information relating to the Northern interior to protect their commercial interests.
Nevertheless, this chart, which was engraved by Thomas Harmar, remains an important achievement in the cartography of the Pacific North West and is fundamental to any collection dealing with the search for the Northwest passage.
(Sources: Kershaw#1140, Wagner#696, BLR#37392, Cohen&Taliaferro Catalogue#62, Campbell A Cook Mystery Solved , Sep.85)