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National Map Accuracy Standards (NMAS)

The U.S. National Map Accuracy Standards (NMAS) define a relationship between map scale and map accuracy. The NMAS were published by the U.S. Bureau of the Budget in 1941 (revised in 1947). U.S. maps that meet the standards contain the text “This map complies with National Map Accuracy Standards.” GIS projects in the United States often use base maps or digital databases with error estimates based on the NMAS.

Map scale is the ratio of distance on a paper map to distance on the surface of the earth. For example, if the distance between points on a map is 1 unit and the equivalent distance on the earth is 24,000 units, then the map scale is 1:24,000. The smallest size point or line width that can ...

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