The Michigan State University Map Library now has on display three copper plates used to make the 1912 USGS topographic map of the Lansing, Michigan area. “From the 1880s to the 1950s, the U.S. Geological Survey used engraved copper plates in the process of printing topographic and geographic quadrangle maps. Copper alloy engraving plates were inscribed with a mirror image of the points, contour lines, symbols, and text that constitute a topographic map. Each plate was inscribed with details for a single color of ink.” [via]