Allen evaluates William Clark’s cartographic achievements, arguing that Clark was one of the most talented and productive mapmakers in American exploration history. The article examines Clark’s surveying methods in the field — his use of dead reckoning, compass bearings, and estimated distances to create remarkably accurate route maps — and the challenges of mapping in difficult terrain without modern instruments. Allen traces the evolution of Clark’s geographic understanding from the expedition’s earliest maps through the comprehensive master map of 1810, which synthesized observations from the outbound and return journeys with information obtained from Native peoples, fur traders, and other sources. The article discusses Clark’s innovations in representing geographic features and his integration of Native geographic knowledge into Western cartographic conventions. Allen argues that Clark’s map of the American West was not surpassed in accuracy for several decades and fundamentally reshaped American understanding of continental geography.
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