FEDERAL COMMUNICATIONS COMMISSION
News media information 202/418-0500,
1919 M STREET N.W.
WASHINGTON, D.C. 20554
Internet http://www.fcc.gov or ftp.fcc.gov
[ 3 FCC Rcd 1478 ] Released March 14, 1988
FCC Interim Procedures for the Specification of Geographic
Latitude and Longitude coordinates (coordinates) are being changed slightly for all points in
the United States. This is a result of the North Americum Datum (NAD 27), on which
the North American coordinates are based, being replaced with the more accurate 1983
North American Datum (NAD 83). This activity is authorized by the Office of
Management and Budget and is being overseen by the Federal Geodetic Control
Committee. Actual calculations are being performed by the National Geodetic Survey (NGS).
The Commission will eventually convert to use of NAD83 to maintain accuracy in our
records and to maintain consistency with other government agencies and foreign
administrations. The conversion to NAD83 will affect coordinates used to describe
communications sites on authorizations, notifications, forms, rules, data bases, etc.
Current topographic maps such as the 7.5 - minute quadrangle maps published by the Geological Survey which are often used by
applicants to determine the coordinates of their site, specify NAD27 in the lower left
corner. At some point in the near future, Geological Survey will begin to issue maps
based on NAD83. Initially, dual sided (NAD27/NAD83) maps will be issued. Eventually, only
NAD83 maps will be available. The satellite-based Global Positioning System (GPS) is already programmed
with NAD83. Site coordinates determined by use of GPS receivers thereof already reflect
In order to prevent intermixing of data using two different datums, the following
procedures will be in effect until further notice:
- Applicants are instructed to furnish coordinated based on the NAD27 datum on all
submissions. Failure to do so could delay the processing of an application.
- Applicants who have filed coordinates based on the NAD83 datum must provide
NAD27 coordinates to the appropriate licensing bureau.
- Until further notice, the Commission will continue to specify NAD27 coordinates
in its data bases, authorizations, notifications, forms, rules, etc.
The Commission will issue further guidance on the conversion to NAD83 as more
information becomes available. For further information, contact [Donald Campbell at the Office of Engineering
and Technology.], (202) - 418 - 2405.
FEDERAL COMMUNICATIONS COMMISSION
--- For all GPS receivers, the internal
native datum is WGS 84 (World Geodetic System of 1984). Many GPS receivers have
internal hardware or software to convert the coordinates between two or more datums.
Thus, GPS measurements should be made in terms of WGS 84. However, for charting,
mapping, and navigation purposes, NAD 83 and WGS 84 are nominally the same
(within a few meters).
--- DO NOT USE THE GPS RECEIVER'S INTERNAL
ROUTINES TO CONVERT FROM WGS 84 / NAD 83 TO NAD 27
COORDINATES! The internal GPS receiver conversion routines only
account for ellipsoidal errors (i.e., errors in how accurately the
Earth's shape is modelled), and NOT survey errors. The NADCON NAD 83 / NAD 27
conversion program accounts for both ellipsoidal AND survey errors.
The horizontal accuracy of GPS receivers is ± 17.8 meters and the vertical
accuracy is ± 27.7 meters.
--- Site coordinates derived from 7.5 minute (1:24,000) USGS paper maps by spotting the
tower / antenna site on the map, and then interpolating the latitude, longitude, and
elevation data from the map, have a horizontal accuracy of no better than ± 12 meters
and a vertical accuracy of ± ½ the contour interval. In the continental U.S., one
second of latitude or longitude is about 30 meters. Assuming that an applicant can
accurately spot the proposed tower / antenna site on a map, decimal seconds cannot be
accurately interpolated from the map.
--- This footnote was not contained in the original Public Notice duplicated above. This
information was added at the suggestion of Donald Campbell at the Office of Engineering
and Technology, FCC to provide greater detail on these matters. You may contact Mr.
Campbell by e-mail or by telephone at (202) - 418 -2405 with any questions.
Please also see the Public Notice released September 1, 1992
entitled The Federal
Communications Commission Continues to Require Applicants to Use Coordinates Based
On The North American Datum of 1927", DA 92-1188, 7 FCC Rcd 6096. A program to convert between
NAD27 and NAD83 datums may be obtained from NOAA's National Geodetic