Clark's Expedition Maps Proved Accurate

In 1803, U.S. President Thomas Jefferson assigned American explorer Meriwether Lewis a mission to find a direct water route to the Pacific Ocean. When the Corps of Discovery departed Camp River, Dubois, Illinois, in 1804, American cartographer William Clark took primary responsibility for mapping the western journey. He used celestial observations, dead reckoning, a surveyor's compass, sextants, and a chronometer, regularly comparing his calculations with Lewis's notes. When the expedition reached the Pacific, Clark's calculation of its total travel distance missed the actual figure by only 40 miles.

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