To Define a Datum

You can define a new datum based on your own data or use a predefined datum as a basis for creating your own.

To define a datum

1. Click Map Setup tabCoordinate System panelCreateCreate Datum Definition.

   Create A Datum is selected. Click Next.

2. On the Specify Datum page of the wizard, select Create A New Datum or Create A New Datum From An Existing Datum and click Next .

   If you are using an existing datum , specify the datum that will be the basis of the new one.

3. On the Create/Modify Datum page, enter a unique code in the Code box.

   The code must be unique and must not contain spaces. Only the following characters are valid: A-Z (upper or lower case), 0-9, dash, and underscore.

4. Enter a description.

   AutoCAD Map 3D toolset displays the description in the Coordinate System Library.

   The remainder of the fields in the wizard are pre-populated if you are using an existing datum. For a new datum, they are blank. In either case, you can specify new values.

5. Specify the following:
   • Ellipsoid: Select the ellipsoid on which this datum will be based.
   • Source: Enter the data source from which the values for this datum were taken.
6. Click Finish.