This document defines the digital map product of the U.S. Geological Survey (USGS) Historical Topographic Map Collection (HTMC). The HTMC is a digital archive of about 190,000 printed topographic quadrangle maps published by the USGS from the inception of the topographic mapping program in 1884 until the last paper topographic map using lithographic printing technology was published in 2006. The HTMC provides a comprehensive digital repository of all scales and all editions of USGS printed topographic maps that is easily discovered, browsed, and downloaded by the public at no cost. Each printed topographic map is scanned “as is” and captures the content and condition of each map. The HTMC provides ready access to maps that are no longer available for distribution in print. A new generation of topographic maps called “US Topo” was defined in 2009. US Topo maps, though modeled on the legacy 7.5-minute topographic maps, conform to different standards. For more information on the HTMC, see the project Web site at: http://nationalmap.gov/historical/.