In 1803, President Thomas Jefferson commissioned an expedition to explore the American Northwest. One important result of this famous expedition led by Meriwether Lewis and William Clark was the mapping of the interior of the US. This Website from Smithsonian's National Museum of Natural History and EdGate.com offers background information, historical context, expedition maps, and educational resources (activities and lesson plans) on Lewis and Clark. The site's cartographic emphasis gives useful tips on mapping techniques and challenges; digital images of the original maps are in the works, and the several available maps are fascinating and well worth the look.