The map was drawn on short notice by Ephraim Gilman, at the time the Principal Draftsman of the General Land Office. Gilman’s map depicts the United States as a trans-continental power, a status achieved with the 1846 Oregon Treaty with Great Britain. This status was cemented in 1848 at the end of the war with Mexico, when in the Treaty of Guadalupe Hidalgo the country gained a vast territory containing Texas and the future states of Arizona, California, Nevada and New Mexico. The map features pastel color by state and territory, with different-colored lines indicating the progressive expansion of American territory by treaty since 1783. Statistical tables at left and right lay out the geographical extent of the states and territories. The simple and seemingly straightforward design efficiently accomplishes Polk’s main rhetorical objective of highlighting the staggering amount of territory gained in the Treaties of Oregon and Guadalupe Hidalgo.
But there’s more, much more: As discussed in an excellent essay written for the National Archives by Stegmaier and McCulley, the map features a striking number of intriguing and controversial inclusions and omissions, as well as ambiguities and outright errors. Among these are several reflecting Polk’s own political views, including the location of Santa Fe in Texas rather than New Mexico; the proposed Minnesota and Nebraska Territories; and the extension to the Pacific of the Missouri Compromise line at latitude 36° 30’ (this last a bone thrown to Southern slaveholders, who had gone ballistic at the so-called Wilmot Proposal, which sought to ban slavery in any territories gained from Mexico.) Two interesting errors are the odd re-naming of the Cumberland and Tennessee rivers to the “Great Kanawha” and the “Big Sandy,’ respectively: Stegmaier and McCulley believe it impossible that a cartographer of Gilman’s status could have made such a mistake and suggest that Gilman, resentful at being asked to produce a complex map on such short notice, was intentionally tweaking President Polk, a Tennessean!
Not in Phillips, Maps of America. Mark J. Stegmaier with Richard T. McCulley, “Ephraim Gilman’s 1848 Map of the United States, Now Expanded Coast to Coast,” in Prologue Magazine, vol. 41 no. 4 (Winter 2009).