Nicollet's map is a landmark in the mapping of the Transmississippi West and one of the most important American maps of the 19th Century. This is the second edition of the map, which accompanied the House edition of Nicollet's report: Report Intended to Illustrate a Map of the Hydrographical Basin of the Upper Mississippi River.
Nicollet's map is the earliest accurate mapping of the interior of North America, from St. Louis north to the Canadian Border, and west along the Missouri River. Covering the region of the Northern Plains and Upper Mississippi River, the map is based upon systematic instrument surveys by the French mathematician and astronomer Joseph Nicollet between 1836 and 1840. Schartz and Ehrenberg comment that "Nicollet's map initiated the scientific mapping of the trans-Mississippi West by the War Department." Rumsey remarks that "the map was years ahead of its time, with its regional concept and sound basis in instrument readings and astronomically determined points." The map is the first to chart the Mississippi River utilizing mathematical calculations to confirm the true source of the Mississippi. In total, Nicollet utilized over 90,000 readings.
Joseph Nicollet compiled the data during his 1839 expedition to the headwaters of the Mississippi ith the Army Corps of Topographical Engineers, the first such expedition organized by the newly reorganized Corps. Nicollet was assisted by John C. Fremont, then on his first assignment as a surveyor and has the distinction of being Fremont's first published survey.