**This article applies to ArcGIS Desktop versions 8.0 through 9.1 only.** Custom geographic (datum) transformations for shapefiles and geodatabase feature classes cannot be used in ArcToolBox, but can be used in ArcMap by completing the steps below.
At versions after 9.1, a custom geographic (datum) transformation can be saved to disk using the Create Custom Geographic Transformation tool in ArcToolbox.
- Open ArcMap with a new, empty map, and add the dataset that has a defined coordinate system that needs to be transformed to a new coordinate system.
- Click View > Data Frame Properties > Coordinate System tab.
- In the 'Select a Coordinate System:' box, open Predefined, select the output coordinate system, and click Apply.
- In the Geographic Coordinate System Warning dialog box that appears, click Yes.
- Click on the Transformations button, and in the Geographic Coordinate System Transformations dialog box, verify that the correct geographic coordinate system is selected in the 'Convert from...' box.
Do not change the GCS listed in the 'Into...' box in this dialog box.
- To the right of the 'Using...' box, click New. From the Method Name drop-down list, select the correct transformation method from the available choices.
- Enter the required parameter values, then click OK on the New Geographic Transformations dialog box. Optionally, the transformation name can be changed.
Be sure to include the correct sign for the transformation parameter values. If the parameter value is negative, the value entered must include the '-' (minus) sign.
- Click OK on the Geographic Coordinate System Transformations dialog box.
- Click OK on the Data Frame Properties dialog box.
- Right-click on the layer name in the ArcMap Table of Contents (TOC). Click Data > Export data > All Features, and change the radio button to 'Use the same coordinate system as the data frame'.
- Set the output location, assign an appropriate name to the new shapefile or feature class, and click OK. The new shapefile or geodatabase feature class will be written in the desired location in the new coordinate system.
To help with similar issues in the future, download the EPSG Geodetic Parameter Dataset of coordinate systems, datum transformation parameters, and get other useful information at the EPSG Web site.
The EPSG (European Petroleum Survey Group) Dataset contains parameters for over 1,800 coordinate systems and over 800 datum transformations, as well as a wealth of other map projection-related information.