Map Accuracy Standards - USGS

Map Accuracy Standards As applied to the USGS positions from aerial photographs. Field Map Accuracy quadrangle topographic map, the hori- survey methods are the only tests An inaccurate map is not a reliable map. zontal Accuracy standard requires that the accepted for official Accuracy testing. X may mark the spot where the trea- positions of 90 percent of all points Positions must be obtained by surveys of sure is buried, but unless the seeker can tested must be accurate within 1/50th of a higher Accuracy . Vertical tests are run locate X in relation to known land- an inch ( centimeters) on the map. At separately to determine precise eleva- marks, the map is not very useful. 1:24,000 scale, 1/50th of an inch is 40 tions. The mapped positions are checked feet ( meters). The vertical Accuracy against the field and (or) photogrammet- The Geological Survey (USGS) standard requires that the elevation of 90 rically determined positions results.

Standards, it is certified and published with the statement that it complies with those standards. By such rigorous testing of some of its maps, the USGS is able to determine that its procedures for collecting map information ensure a high level of map accuracy. Factual Errors There are other kinds of errors in mapmaking. Names and symbols of

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