3.1: What are the United States map accuracy standards?
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This article is from the Geographic Information Systems FAQ, by Lisa Nyman lnyman@census.gov with numerous contributions by others.
3.1: What are the United States map accuracy standards?
From: rcw@scicom.AlphaCDC.COM (Robert White)
United States National Map Accuracy Standards
With a view to the utmost economy and expedition in producing maps
which fulfill not only the broad needs for standard or principal maps,
but also the reasonable particular needs of individual agencies,
standards of accuracy for published maps are defined as follows:
1. 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 1/30 inch, measured on the publication scale; for
maps on publication scales of 1:20,000 or smaller, 1/50 inch. These
limits of accuracy shall apply in all cases to positions of well-
defined points only. Well-defined points are those that are easily
visible or recoverable on the ground, such as the following:
monuments or markers, such as bench marks, property boundary
monuments, intersections of roads, railroads, etc.; corners of large
buildings or structures (or center points of small buildings); etc.
In general what is well defined will also be determined by what is
plottable on the scale of the map with 1/100 inch. Thus while the
intersection of two road or property lines meeting at right angles
would come within a sensible interpretation, identification of the
intersection of such lines meeting at an acute angle would obviously
not be practicable within 1/100 inch. Similarly, features not
identifiable upon the ground within close limits are not to be
considered as test points within the limits quoted, even though
their positions may be scaled closely upon the map. In this class
would come timber lines, soil boundaries, etc.
2. Vertical Accuracy, as applied to contour maps on all publication
scales, shall be such that not more than 10 percent of the
elevations tested shall be in error more than one-half the contour
interval. In checking elevations taken from the map, the apparent
vertical error may be decreased by assuming a horizontal
displacement within the permissible horizontal error for a map of
that scale.
3. The accuracy of any map may be tested by comparing the positions of
points whose locations or elevations are shown upon it with
corresponding positions as determined by surveys of a higher
accuracy. Tests shall be made by the producing agency, which shall
also determine which of its maps are to be tested, and the extent of
such testing.
4. Published maps meeting these accuracy requirements shall note this
fact on their legends, as follows: "This map complies with National
Map Accuracy Standards."
5. Published maps whose errors exceed those afore stated shall omit from
their legends all mention of standard accuracy.
6. When a published map is a considerable enlargement of a map drawing
(manuscript) or of a published map, that fact shall be stated in the
legend. For example, "This map is an enlargement of a
1:20,000-scale map drawing," or "This map is an enlargement of a
1:24,000-scale published map."
7. To facilitate ready interchange and use of basic information for map
construction among all federal map making agencies, manuscript maps
and published maps, wherever economically feasible and consistent
with the uses to which the map is to be put, shall conform to
latitude and longitude boundaries, being 15 minutes of latitude and
longitude, or 7.5 minutes or 3-3/4 minutes in size.
US Bureau of the Budget
Issued June 10, 1941
Revised April 26, 1943
Revised June 17, 1947
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