U.S. National Map Accuracy Standards for Horizontal Accuracy
Explains federal standards for determining horizontal ground accuracy of geospatial data
According to the United States National Map Accuracy Standards of the National Mapping Program (NMP) , the standard for horizontal accuracy is as follows:
- Horizontal accuracy. For maps on publication scales larger than 1:20,000, not more than 10 percent of the points tested shall be in error by more than 1/30th inch, measured on the publication scale; for maps on publication scales of 1:20,000 or smaller, 1/50th inch.
- For maps of larger scale than 1:20,000, at least 90% of the tested points must be within 1/30 inch (.03333 inch). For maps of 1:20,000-scale or smaller, at least 90% of the tested points must be within 1/50th inch (.02 inch).
- If larger than 1:20,000-scale, use this calculation:
.03333 x scale x 2.54 / 100 = ground meters.
- If 1:20,000-scale or smaller, use this calculation:
.02 x scale x 2.54 / 100 = ground meters.
- For 1:100,000-scale maps:
.02 x 100,000 x 2.54 / 100 = 50.8 meters (or 166 ft)
- For 1:24,000-scale maps:
.02 x 24,000 x 2.54 / 100 = 12.2 meters (or 40 ft)
Conversion table for each scale:
|Map Scale||Ground Meters|