If the source and destination coordinate systems use different datums, AutoCAD Map 3D toolset 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 toolset 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 toolset uses version 2.
Danger: 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.