Ever since somebody first wondered how to get from here to there and a know-it-all roughed out a route in the dirt with a stick, there have been maps, and the Maps and Minds exhibit at the National Geographic Society in Washington, D.C. is celebrating that history with more than 500 photographs and drawings on cartography through the ages. The occasion is the 100th anniversary of the plan by John Wesley Powell, a co-founder of the society, to map the U.S. topographically. But the exhibit's examples are worldwide, showing how the Portuguese drew maps on animal skins, the Eskimos carved them on ivory, and the Marshall Islanders employed shells. The oldest map in the show is a Babylonian clay tablet from 2500 B.C. showing a city. There is a section on Greek map-makers, including Eratosthenes, who estimated the circumference of the world at 25,000 miles, less than 200 miles off. There's a 13th-century equivalent of the Michelin Guides, a list of stopping places for Christian pilgrims on their way from London to the Holy Land. There is even a chart of Haiti drawn by Columbus in 1492. The exhibit, co-sponsored by the U.S. Geological Survey and the National Geographic Society, focuses on American mapmakers, who have included George Washington, Daniel Boone, Benjamin Franklin and Paul Revere. The show is fascinating and informative, though the captions are sketchy at times. A discussion of the Lewis and Clark Expedition maps of the Louisiana Territory drawn in 1804-06, for instance, mentions Meriwether Lewis died "under suspicious circumstances" but doesn't explain that his death in 1809 was either suicide or murder. The exhibit will remain in Washington through September and then travel around the country.