The full dimensions of this map as it appeared in the 1763 and 1774 editions are 11-7/16 inches high by 13-5/8 inches wide. The scale is 1:8,500,000.

--J.M.

Some years before Jefferson was elected president, this part of Louisiana had become a focus of intense political concern, especially regarding the location of the boundary between Spanish and U.S. territory, and the route to Santa Fe. Jefferson sent two separate exploratory expeditions into this arena while Lewis and Clark were still en route through the Northwest. One, led by Jefferson's American Philosophical Society colleague, William Dunbar, made a short trip up the Ouachita River—du Pratz's Black River—in 1804. The other was the ill-fated Freeman-Custis Expedition up the Red River in the spring and summer of 1806.

William Clark was familiar with the Ohio and Mississippi Rivers well before he joined Lewis on the expedition to the Pacific. In 1795 he commanded a "barge"—perhaps similar to the one Lewis ordered built for his exploration of upper Louisiana—with a company of seventeen soldiers on a diplomatic mission to the Spanish authorities at Chickasaw Bluffs, and three years later he piloted a flatboat-load of tobacco from the Clark plantation at the Falls of the Ohio, down to New Orleans.

—J.M.