David Thompson (30 April 1770 – 10 February 1857) was a British fur trader, surveyor, and cartographer, known to some native people as "Koo-Koo-Sint" or "the Stargazer". Over Thompson's career, he travelled 90,000 kilometres (56,000 mi) across North America, mapping 4.9 million square kilometres (1.9 million square miles) of the continent along the way. For this historic feat, Thompson has been described as the "greatest practical land geographer that the world has produced".
David Thompson was born in Westminster, Middlesex, to recent Welsh migrants from Radnorshire David and Ann Thompson. They changed their family name from ap Thomas to Thompson. When Thompson was two, his father died. Due to his widowed mother not having financial resources, she placed Thompson, 29 April 1777, the day before his seventh birthday, and his older brother in the Grey Coat Hospital, a school for the disadvantaged of Westminster. Thompson graduated to the Grey Coat mathematical school, well known for teaching navigation and surveying.
He received an education for the Royal Navy: including mathematics of trigonometry and geometry, practical navigation including using of nautical instruments, finding latitudes and longitudes and making navigational calculations from observing the sun, moon and tide, and drawing maps and charts, taking land measurements, and sketching landscapes. He later built on these skills to make his career. In 1784, when Thompson was 14, the Grey Coat treasurer paid the Hudson's Bay Company the sum of five pounds, upon which the youth became an apprentice employee of the company, contracted for a period of seven years to be trained as a clerk. In fact, two students had been selected for apprenticeships, but the other child was so scared of moving to the wilderness that he ran away, leaving just Thompson to take the position.
He set sail on a ship to North America on 28 May of that year, leaving England.
On 2 September 1784, Thompson arrived in Churchill (now in Manitoba) and was put to work as a clerk/secretary, copying the personal papers of the governor of Fort Churchill, Samuel Hearne. The next year he was transferred to nearby York Factory, and over the next few years spent time as a secretary at Cumberland House, and South Branch House of the Hudson's Bay Company before being transferred to Manchester House in 1787. During those years he learned to keep accounts and other records, calculate values of furs (it was noted that he also had several expensive beaver pelts at that time even when a secretary's job would not pay terribly well), track supplies and other duties.
In addition to clerical duties, Thompson began seeking out field missions. In 1786, he joined a group of traders heading south and west on the Hayes River, crossed Lake Winnipeg, went up the Saskatchewan River, and made it to the foothills of the Rocky Mountains. He returned to the Rockies on a trade mission the following year to meet with the Piegan Blackfeet Indians. Thompson wintered with the tribe, learned their language, and established lifelong friendships.
On 23 December 1788, Thompson seriously fractured his tibia, forcing him to spend the next two winters at Cumberland House convalescing. It was during this time that he greatly refined and expanded his mathematical, astronomical, and surveying skills under the tutelage of Hudson's Bay Company surveyor Philip Turnor. It was also during this time that he lost sight in his right eye.
While sitting alone one winter day in front of a chequerboard, Thompson wrote in his diary that the devil showed up and took the seat opposite him, and the two played numerous games, all of which the devil lost. Then, all at once, he was alone again. Whether it was a dream or a hallucination, he didn't say, but David Thompson became a staunch Christian after the experience and remained so for the rest of his life.
In 1790, with his apprenticeship nearing its end, Thompson requested a set of surveying tools in place of the typical parting gift of fine clothes offered by the company to those completing their indenture. He received both. He entered the employ of the Hudson's Bay Company as a fur trader. In 1792 he completed his first significant survey, mapping a route to Lake Athabasca (where today's Alberta/Saskatchewan border is located).
Between February and May 1793, Thompson made 34 observations of the longitude of Cumberland House using lunar distances. The mean of these observations was 102°12′ W, about 2′ east of the modern value. The mean error of the 34 observations was about 15′ of longitude. Broughton (2009) notes that the precision of the type of sextant used by Thompson was 15″ of arc, corresponding to 7.5′ of longitude giving an absolute limit to the precision of an individual observation. The error in Thompson's mean was several times less than this. The time he took on these observations, about 3 hours of calculation each, indicates that he understood the power of averages.
In recognition of his map-making and surveying skills, Thompson was promoted to official surveyor of the Hudson’s Bay Company in 1794. He continued working for the Hudson's Bay Company until 23 May 1797 when, frustrated by an order to cease surveying and focus on the fur trade, he left. He walked 130 kilometres (80 mi) in the snow in order to enter the employ of the competition, the North West Company. There he continued to work as a fur trader and surveyor.
Thompson's decision to defect to the North West Company (NWC) in 1797 without providing the customary one-year notice was not well received by his former employers. But the North West Company was more supportive of Thompson pursuing his work on surveying and mapping the interior of what was to become Canada, as they judged it in the company's interest to know the exact locations of their settlements and the distances between them. In 1797, Thompson was sent south by his employers to survey part of the Canada-US boundary along the water routes from Lake Superior to Lake of the Woods to satisfy unresolved questions of territory arising from the Jay Treaty of 1794 between Great Britain and the United States after the American Revolutionary War.
By 1798 Thompson had completed a survey of 6,750 km (4,190 mi) from Grand Portage, through Lake Winnipeg, to the headwaters of the Assiniboine and Mississippi rivers, as well as two sides of Lake Superior. In 1798, the company sent him to Red Deer Lake (Lac La Biche in present-day Alberta) to establish a trading post. (The English translation of Lac la Biche: Red Deer Lake, was first recorded on the Mackenzie map of 1793.) Thompson spent the next few seasons trading based in Fort George (now in Alberta), and during this time led several expeditions into the Rocky Mountains.
On 10 July 1804, at the annual meeting of the North West Company in Kaministiquia, Thompson was made a full partner of the company. He became a 'wintering partner', who was based in the field rather than Montreal, and was granted two of the 92 NWC's shares worth more than £4,000. He spent the next few seasons based there managing the fur trading operations, but still finding time to expand his surveys of the waterways around Lake Superior. At the 1806 company meeting, officers decided to send Thompson back into the interior. Concern over the United States-backed expedition of Lewis and Clark prompted the North West Company to charge Thompson with the task of finding a route to the Pacific to open up the lucrative trading territories of the Pacific Northwest.
After the general meeting in 1806, Thompson travelled to Rocky Mountain House and prepared for an expedition to follow the Columbia River to the Pacific Ocean. In June 1807 Thompson crossed the Rocky Mountains and spent the summer surveying the Columbia basin; he continued to survey the area over the next few seasons. Thompson mapped and established trading posts in Northwestern Montana, Idaho, Washington, and Western Canada. Trading posts he founded included Kootenae House, Kullyspell House and Saleesh House; the latter two were the first trading posts west of the Rockies in Idaho and Montana, respectively. These posts established by Thompson extended North West Company fur trading territory into the Columbia Basin drainage area. The maps he made of the Columbia River basin east of the Cascade Mountains were of such high quality and detail that they continued to be useful into the 20th-century.