David Thompson’s Surveying and Mapping of the Northwest of North America

David Thompson surveyed and mapped a vast region of the Northwest of North America, stretching from the 45th parallel to the 60th parallel and from the western shores of Hudson Bay and Lake Superior to the Pacific Ocean between 1790 and 1812. Often accompanied by his Métis wife, Charlotte Small, he travelled 50,000 miles by canoe, horseback and on foot, making hundreds of astronomical observations to accurately determine the geographical positions of fur-trading posts and major natural landmarks – while attending to the day-to-day business of fur trading for the Hudson’s Bay and North West Companies. 

At age 14 Thompson was indentured to the Hudson’s Bay Company (HBC), arriving at Fort Churchill in 1784 to work as a clerk. In 1788 he severely fractured his right tibia and, while recuperating at Cumberland House, learned surveying skills from HBC astronomer Philip Turnor. At this time, he lost sight in his right eye, leaving one of history’s greatest surveyors with a serious visual impairment.

Thompson joined the North West Company in 1797, helping the company expand its operations by, in his first year alone, mapping the Assiniboine River Basin and the Mandan villages of North Dakota, locating the source of the Mississippi River, and circumnavigating Lake Superior. Between 1807 and 1812 he established a viable northern trade route to the Pacific Ocean, solving the puzzle of the Columbia River basin including six of its tributaries, and becoming the first European to travel the entire course of the Columbia River.

In addition to Thompson’s connection to the Cree people through his wife, he enjoyed excellent relations with many other First Nations peoples. He spoke at least four indigenous languages – Blackfoot, Kootenay, Chipewyan, and Mandan. The Salish bestowed him with the name Koo-Koo-Sint: “Man Who Looks at Stars”. He also strongly opposed the practice of trading posts exchanging alcohol for furs.

Thompson’s legacies include his 1814 Great Map, compiled from his surveys and those of Alexander Mackenzie, Simon Fraser, George Vancouver, and his mentor, Philip Turnor, that laid the groundwork for development of the Northwest of North America. J.B. Tyrrell found, transcribed and edited his 702-page, handwritten manuscript describing his travels, publishing it in 1916 as David Thompson’s Narrative of his Travels in Western America 1784-1812.  It included extensive original data on the geological, botanical, zoological, anthropological, and meteorological facets of the regions he had visited.