Tools that honor the Geographic Transformations environment will use the transformation methods when projecting data.
Specify transformation methods that can be used to project data on the fly. You can create a list of transformation methods the application can use, including custom transformations (those created using the Create Custom Geographic Transformation tool) and system-supplied transformations (those out of the box).
When working with geographic transformations, if the direction is not indicated, geoprocessing tools will apply the directionality automatically. For example, if converting data from WGS84 to NAD 1927, you can use the NAD_1927_to_WGS_1984_3 transformation, and the software will apply it correctly.
Usage notes
- When using a geoprocessing tool in an ArcGIS AllSource project with an open map that is using map transformations, the tool will use the map transformations. If the map transformations are not valid for the data, they will be ignored. In this situation, transformations specified in the environment will take priority over map transformations. However, if the transformation in the environment is not valid for the data being processed by a tool, and the map transformation is valid, the map transformation will be used.
- You can include out-of-the-box transformation methods, those supplied with the application, those in the list, and custom transformation methods created using the Create Custom Geographic Transformation tool.
- A tool will only use transformations appropriate to the projection, all other transformations will be ignored.
- The environment supports composite transformation methods. The Project tool's transformation parameter and the arcpy.ListTransformations function provide valid transformations, for example, ITRF_2000_To_WGS_1984 + ITRF_2000_To_NAD_1983_2011.
- If a projection requires multiple transformation methods, including composite, a tool will only use a single transformation from the environment. This is the case even if multiple transformation methods have been set. If a projection requires more than one transformation method, use the Project tool.
Dialog syntax
Available transformations include system-provided transformations and custom transformations created using the Create Custom Geographic Transformation or Create Custom Vertical Transformation tools tools.
To specify a transformation, provide a transformation name or select an option from the choice list.
Click the Select transformation button 
to open the Transformation window. Click the Add button, and set the Source coordinate system and Target coordinate system values. After the source and target coordinate systems are defined, select a Transformation path value that is valid between the two coordinate systems, and click OK. The source and target coordinate systems must be in the geographic coordinate systems between which a transformation will be applied.
Scripting syntax
arcpy.env.geographicTransformations = geographic_transformations
| Parameter | Explanation |
|---|---|
geographic_transformations | A semicolon-delimited string of transformation methods. This can include system-provided transformation methods as well as custom transformation methods created using the Create Custom Geographic Transformation tool. |
Script example
Project data into a new coordinate system while buffering.
import arcpy
# Set the workspace, outputCoordinateSystem and geographicTransformations
# environments
arcpy.env.workspace = "c:/data"
arcpy.env.outputCoordinateSystem = arcpy.SpatialReference("WGS 1984 UTM Zone 18N")
arcpy.env.geographicTransformations = "Arc_1950_To_WGS_1984_5; PSAD_1956_To_WGS_1984_6"
arcpy.analysis.Buffer("roads.shp", "roads_buffer.shp", "10 meters")