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:
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 be determined by what is plottable on the scale of the map within 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.
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.
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 the testing.
Published maps meeting these accuracy requirements shall
note this fact on their legends, as follows: "This map complies with National Map accuracy Standards."
Published maps whose errors exceed those aforestated shall
omit from their legends all mention of standard accuracy.
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."
To facilitate ready interchange and use of basic information for
map construction among all Federal mapmaking 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.
U.S. BUREAU OF THE BUDGET
Issued June 10, 1941
Revised April 26, 1943
Revised June 17, 1947