One of Thomas Jefferson's major objectives in sending Meriwether Lewis and William Clark on their heroic adventure to the Pacific Coast was to map the vast, unknown region acquired through the Louisiana Purchase.

In an illustrated lecture, Ralph E. Ehrenberg will discuss the extent of the geographical knowledge of the Trans-Mississippi West on the eve of the expedition, the role of Indian maps in planning the expedition and guiding the explorers, the preparation of survey route maps and post expedition composite maps by Clark, and their contributions to the mapping of the West. For an on-line preview of Mr. Ehrenberg's writing on this subject, see http://www.edgate.com/lewisandclark/mapping_on_trail.html.

Mr. Ehrenberg writes and lectures on cartographic and geographic resources, the history of cartography, and the management of cartographic collections. During a thirty-seven year career with the Federal Government he has worked as an aerial photographer, a cartographer, and a map curator.

From 1973 to 1998, Mr. Ehrenberg directed two of the most important cartographic collections in world - the Cartographic Archives Division of the U.S. National Archives and Records Administration and the Geography and Map Division of the Library of Congress.

Mr. Ehrenberg's major publications include Library of Congress Geography and Maps: An Illustrated Guide (Washington, D.C.: Library of Congress, 1996); Scholars' Guide to Washington, D.C. for Cartography and Remote Sensing Imagery (Washington, D.C.: Smithsonian Institution Press, 1987); and The Mapping of America, with Seymour Schwartz (New York: Harry N. Abrams, Inc., 1980, 2001).