Canadian Coast Guard

CANADIAN HYDROGRAPHIC SERVICE - Conversion of charts to North American Datum 1983 (NAD 83)

The Canadian Hydrographic Service is converting navigational charts to the North American Datum 1983 (NAD 83).

NAD 83 is considered equivalent to the World Geodetic System 1984 (WGS 84) recently adopted as the horizontal datum for world-wide use. The advantage of the new datum is its compatibility with the NAVSTAR (GPS) satellite positioning system.

The difference in the position of the same point when quoted on the former NAD 27 and the new NAD 83 is up to 60 metres on the Atlantic coast, about 110 metres on the Pacific coast and almost zero near Chicago although there can be local discrepancies from these approximations.

Horizontal positions obtained from satellite receivers are based on NAD 83 (WGS 84) and must be converted to the horizontal chart datum (if not NAD 83) before being used. In some cases, the horizontal position obtained by LORAN-C coordinate converters, after due correction for Additional Secondary Factor (see Part 6), is based on NAD 83 and must also be converted to horizontal chart datum (if not NAD 83).

A note has been added to nearly all existing charts indicating the datum on which the chart is based, and providing the increase or decrease required to convert the latitude and longitude from NAD 83 to the chart datum.

New Charts and New Editions being produced are now almost always based on NAD 83.

Latitude and longitude positions given in this publication are in NAD 27 unless otherwise indicated.