Datum Shift Issues for North American Users
Concept Procedure
 
 
 

If the source and destination coordinate systems use different datums, AutoCAD Map 3D automatically performs a datum shift. Within North America, this is most often a shift between the NAD27 and NAD83 datums.

For United States users, AutoCAD Map 3D uses the freely distributable NADCON grid data files supplied by USGS.

Canadian users can use either version 1 or version 2 of the Canadian National Transformation supplied by Geomatics Canada. If both versions of the Canadian National Transformation are present, AutoCAD Map 3D uses version 2.

Warning Geomatics Canada no longer supports version 1, and many Canadian provinces do not consider it to produce valid results. If you are in Canada and doing NAD Shifts, it is recommended that you use version 2.
See Also