The first postal map stamp issued by the United States was issued in 1904 to commemorate the centennial of the Louisiana Purchase. It is based on a U.S. Land Office Map and shows a map of the United States with the Louisiana Territory shaded.
     The northwestern border of the Louisiana Purchase with Canada was not the 49th parallel as shown on the stamp. Instead it extended north of that parallel, while Canada intruded into northern Minnesota and North Dakota. These departures from the 49th parallel were mutually ceded in the Convention between Great Britain and the United States in 1818, so that from the Stony Mountains to the Lake of the Woods, the border follows the 49th parallel. Another error is the claim of territory in Spanish Florida. The United States acquired Florida from Spain by the Adams-Onís Treaty of 1819.