You need to create a new Coordinate System with the correct datum information. To do this, follow these steps:
Note: You will need the correct information for your new coordinate system, for instance:
- Projection type: Lambert Conformal Conic
- Datum: NAD 1927
- Spheroid: Clarke 1866
- Central meridian: -78°
- First standard parallel: 33°
- Second standard parallel: 45°
- Latitude of origin: 0°
- Units: meters
1. Under Map Setup ribbon look for the Create New Coordinate System (MAPCSCREATE) command.
2. The Create Coordinate System will wizard will display:
3. Select the “Ceate a coordinate system definition” option and cick Next >.
4. Under the Specify starting point, select “Start with a datum” and click Next >.
5. For Specify datum, select “Create a new datum from and existing datum”, click the Select button and browse for the specific datum that you need to modify. (e.g. NAD27 (NAD 1927, mean Values, Continental United States)) and click Next >.
6. For Modify datum; under Code give it a new name (e.g. NAD27_Custom), it is a good practice if you add a description as well and then click Next >.
7. Under Specify coordinate system, use “Create a new coordinate system” and for Coordinate system type select “Projected” from the pull down list and click Next >.
8. Name and create the code for your new coordinate system, you must give it a Description; name the Source, specify the Unit, select the Categories associated with this new CS, for Reference To use “Non-geodetic” and click Next >.
9. Specify the correct projection from the Projection pull down list, acording with your new coorsinate system and populate all the Parameters with the correct information and click Next >.
10. Specify the information for your scaling in paper, use 1 for Map (paper) scale, leaving everything else the same and click Next >.
11. Review the New CS information and click Finish.
Now your new CS will show under CS Library and you can assign it to any drawing or data.