David Thompson

Explorer, astronomer, cartographer

         David Thompson arrived in the Americas as a teen-age boy apprenticed to the Hudson Bay Company.  This precocious lad was taught celestial navigation by master at his first trading post near Hudson's Bay.   At 18, Thompson made his first expedition to the Rocky Mountains and spent the winter living with a Cree chief and his family.  His mastery of astronomy and mapmaking soon made him "the greatest geographer of his day" in British America, and a peerless maker of maps.

          Thompson would go on to map most of the Canadian (and American) West, and it was his work that established the 49th parallel that divided the two countries when that issue was finally settled.  He also found the source of the Columbia River.

           No one knew the western mountains better than Thompson.  After spending decades taking sun sights and painstakingly recording his observations, Thompson produced a remarkably detailed map which he labeled, simply, 'Map of the North-West Territory of the Province of Canada from actual survey during the years 1792-1812.'  Cartographic historian Carl L. Wheat has called this map "one of the greatest maps ever drawn, and a magnificent cartographic monument to its maker."  Thompson's maps are Canadian national treasures and are kept in the national archives in Ottawa, Ontario.

          Thompson was probably the last to see the Indian civilizations of the high plains in a condition of wholeness that existed prior to the arrival of Lewis and Clark.  When the Corps of Discovery started up the Missouri River in 1804, they carried a copy of the chart Thompson had made on previous visits to the Mandan Villages.  They also carried the most up-to-date map of North America that was available at the time -- the Arrowsmith map (see other reference under 1795).  Arrowsmith's "New and Elegant Atlas", published in Philadelphia in 1795, drew heavily from information gathered by Thompson.   Lewis and Clark carried another map of the Missouri to the Mandan Villages, drawn by John Evans, a Welshman, who ascended the river with his boss, James Mackay, in 1787, when both men were employed by the North West Company.   This evidence is cited here to simply point out that the Americans knew where they were going.  In fact, they were following in the footsteps of twenty-five previous expeditions to the Mandan Villages, a fact seldom mentioned in popular accounts the Corps of Discovery.

          The contributions of Thompson, Mackenzie, Evans and Mackay to the Lewis and Clark expedition cannot be overestimated.  Most of the notable geographic landmarks between St. Louis and the Rocky Mountains, and along the West Coast, had already been mapped by 1804.   Mackay, in fact, had been a primary source of information for the Spanish, who made a map highlighting northern rivers and the features of the British fur-trading network in Canada.  The gap in their knowledge is represented in a Spanish map drawn in 1785 that shows a narrow corridor of land running north and south between the west slope of the Rocky Mountains and the great Cascade range, to the west.  Everything in between is marked 'unknown lands, with the following notation: "The black line on this map marks the line between the United States and Canada as observed by Mr. Mackay during his journeys of discovery for the English fur trade in 1784.'

          The original Spanish map was prepared to assist the Spanish explorer Jean Baptise Truteau, when he led an expedition op the Missouri in 1794.  His expedition gives an accurate description of a river that joins the Missouri from the south, above the 'great bend near the Canadian border, which he labeled as The Rock River.  Today we know it as the Yellowstone.

         David Thompson arrived in the Americas as a teen-age boy apprenticed to the Hudson Bay Company.   His mastery of astronomy and mapmaking soon made him "the greatest geographer of his day in British America, and a maker of what was they by far its greatest maps."

(For more on this legendary cartographer, see Sources of the River, by Jack Nesbitt)