Transcription of Map Accuracy Standards - USGS
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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.
each contour interval as a method of controlling overall quality. It is rare for a 7.5-minute map to fail the test, but this happens on occasion. In testing a map, the USGS experts select 20 or more well-defined points; a typical point would be the intersection of two roads. Positions are established on the test points by field teams using sophis-
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