Topographic Maps for Construction Planning

In the overall process of construction planning, topographic maps of different scales, accuracies, and content are needed for different phases of the planning. General-purpose maps published by the U.S. Geological Survey usually meet the need in the reconnaissance and preliminary design phases. About 75% of the area of the United States has topographic map coverage at scales of 1:24,000 or 1:62,500; complete coverage is available only at 1:250,000. Many existing maps, however, are obsolete because the rate of change of mapworthy detail far outstrips the availability of resources for an adequate revision program. The USGS is producing about 2,000 new 7-1/2-min 1:24,000-scale maps per year, but about 30,000 quadrangles have never been mapped in that format. The current map-production rate is about three times that of the late 1940's, due mainly to the application of new techniques. Further improvements in mapping technology offer the best hope for meeting the growing demand for topographic maps.