Exploratory surveying and mapping of the Mississippi's headwaters: 1798-1838

During the late 18 ^th and early 19 ^th centuries, five expeditions to the headwaters of the Mississippi River attempted to determine the global positions of important places and improve the accuracy of maps of the region. The surveyors who either led or accompanied these expeditions were David Thompson, Zebulon Pike, David Douglass, James Allen, and Joseph Nicollet. This article first outlines the methods of exploratory surveying used by these men, and then discusses each expedition with respect to three issues: the efforts, successful and unsuccessful, to accurately determine global positions, the support provided by knowledge from resident Native Americans and fur traders, and the political or strategic backgrounds to the expeditions.