U.S. Army Topographical Engineer Lieutenant William H. Emory's map was a compilation of the best information available in Washington, D.C., on what became the American Southwest before the war with Mexico. Emory's map at first served primarily as a reference tool in U.S. negotiations with the Republic of Texas over the issue of annexation, but Emory himself had not yet visited Texas (although he would soon pass through what became the panhandle with Kearny's Army of the West and would later head the U.S. Mexican Boundary Survey after the war). Emory used and cited the best sources available, including information obtained from maps by Humboldt, Pike, Long, Fremont, the U.S. Boundary Commission Survey of 1825, Austin, Arrowsmith, Kennedy, and Mitchell. Despite this, "Passo del Norte" is still too far east (by one and a half degrees of longitude) thus making the area of present far west Texas much too compressed. Emory acknowledged the dearth of information by delineating two sites for "Presidio de Rio Grande" and noting that "of the two positions given? no information can be obtained to decide which is correct." The map shows routes of American military and civilian pathfinders in the west, including Pike (1806), Long (1819-1821), Gregg (1839), and Fremont (1842). Martin & Martin, Maps of Texas and the Southwest, p. 129; Wheat, Mapping the Trans-Mississippi West, vol. 2, no. 478.
