Mapping the Way

President Thomas Jefferson provided instruments for determining geography by celestial observation, and the data collected by Lewis and Clark shows their skillful use of navigational equipment. The Corps of Discovery carried the most advanced navigational tools available and used them chiefly to calculate latitude and longitude, distance traveled, and the difference between true north and magnetic north, rather than to find their route. To navigate the waterways to the Pacific Ocean, they relied on talks with Indians, intuition, and keen observational skills. They passed through what is now Montana without meeting any native people until Lewis met the Shoshone in present-day Idaho on August 13th 1805. Several days later, the expedition camped with the Shoshone at Camp Fortunate and traded for horses. At river confluences, they used information gained from Indians they had previously encountered, combined with their general knowledge of river systems. The amount of water flow, the nature of the terrain, luck, and instinct helped determine which current they followed. The basic principles of navigation have remained largely unchanged, combining recognizable land features, advice from past travelers, instruments, maps, and sometimes celestial observation to guide travelers toward their destination.

Montana · United States