Allen provides a sweeping survey of the cartographic knowledge and misconceptions that shaped the Lewis and Clark Expedition’s understanding of western geography. The article traces the evolution of European and American maps of the continent from the early 16th century, highlighting how persistent geographic myths — including the imagined “height of land” where major rivers originated in close proximity — influenced Jefferson’s instructions and Lewis’s expectations. Allen examines the specific maps Lewis and Clark carried, including those produced by the Mackay-Evans expedition, Aaron Arrowsmith, and Nicholas King, and how these maps both aided and misled the explorers. The article culminates with an analysis of William Clark’s magnificent 1810 master map, which synthesized the expedition’s observations with information from Native peoples to produce the most accurate map of western North America yet created.
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