FCC Public Notice

1919 M STREET N.W.

News media information 202/418-0500, Fax-On-Demand 202/418-2830,
Internet http://www.fcc.gov or ftp.fcc.gov

DA 88-316         [ 3 FCC Rcd 1478 ]         Released March 14, 1988

FCC Interim Procedures for the Specification of Geographic Coordinates

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 NAD83. (Footnote)

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.



--- 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 Survey.