Rare large scale of the United States published in 1820 showing the extent of inland knowledge up to and including the expeditions of Lewis and Clark. The states up to the 'Missouri Territories' are shown.
During the first decade of the nineteenth century, the geographic image of western North America began to change dramatically. Based on the observations of Lewis and Clark, information gathered from native people, and Clark's own cartographic imagination, this image evolved from an almost empty interior with a hypothetical single mountain range serving as a western continental divide, to an intricate one showing a tangle of mountains and rivers. A continent that had once seemed empty and simple was now becoming full and complex.
It would take another fifty years after Lewis and Clark to complete the cartographic image of the West we know today. Other explorers and map makers followed, each revealing new geographic and scientific details about specific parts of the western landscape. But this revealing process was not a simple one.
Source Library of Congress.