These maps are also called 7.5 minute quadrangles, covering 7.5 minutes of latitude by 7.5 minutes of longitude. Each quadrangle has a place name. Vermont, New Hampshire, and Alaska maps are filed by their names. Maps for other states and U.S. territories are filed by alphanumeric codes. Index grid sheets are available for all states.
All series have indexes.
Most topographic maps are produced by the U.S. Geological Survey, for which the Map Room serves as a depository. The library is also a depository for Canadian topographic maps. Index grid sheets give the designation and location of each map. They are produced by a variety of government agencies, in addition to the U.S. Geological Survey, such as the Forest Service, Bureau of the Census, National Ocean Service, National Park Service, Central Intelligence Agency, Federal Energy Regulatory Commission, and Soil Conservation Service. Thematic maps are also published by businesses and organizations.