HowTo: Apply a geographic (datum) transformation

Article ID:	17430
Software:	ArcGIS - ArcEditor 8.1, 8.1.2, 8.2, 8.3, 9.0, 9.1, 9.2, 9.3 ArcGIS - ArcInfo 8.1, 8.1.2, 8.2, 8.3, 9.0, 9.1, 9.2, 9.3 ArcGIS - ArcView 8.1, 8.1.2, 8.2, 8.3, 9.0, 9.1, 9.2, 9.3
Platforms:	N/A

Summary

ArcMap will automatically try to convert the coordinate systems of any data layers to the Data Frame's coordinate system. If the geographic coordinate systems are not the same, ArcMap needs to do a geographic (datum) transformation. This transformation is not automatically applied because many or no possibilities may exist. Geographic transformations use methods with different accuracies or are defined for particular areas. This document discusses how to manually set a geographic transformation

Procedure

Open the Data Frame properties dialog.
Switch to the Coordinate System tab.
Click the Transformations button on the right side of the panel. The Geographic Coordinate Systems Transformations dialog box will appear.

The 'Convert from' box lists the geographic coordinate systems of the layers. The 'into' dropdown lists has the Data Frame geographic coordinate system. The 'using' dropdown lists any predefined transformation between the two systems.

Don't worry if the transformation name goes in the opposite direction. ArcMap will apply the transformation correctly.
Select one of the listed transformations, or click New to define a custom transformation.

You must set a transformation for each of the coordinate systems listed in the 'Convert from' list box.

Currently, it is not possible to save custom geographic transformations.

Created: 3/22/2001
Last Modified: 7/7/2009