I have some data in Provisional South American Datum 1956, and I need to project it to Web Mercator with WGS84 as the datum.

When I use the project tool in ArcGIS desktop, it requires a Geographic Transformation, and offers me 13 different ones: from PSAD_1956_to_WGS_1984_1 to PSAD_1956_to_WGS_1984_13

How do I find out which is the transformation meant for my area?

I remember finding a pdf on the Esri Forums several years ago, which showed the various transformations between NAD 83/27 & WGS 84.

Is there something similar for all transformations in ArcGIS?

2 Answers 2


There is an excellent blog post on this topic here: About geographic transformations and how to choose the right one

You can find the list of all transformations and their Areas of use, at the bottom of this ESRI Knowledge Base article: HowTo: Select the correct geographic (datum) transformation when projecting between datums


Take a look at the Documentation folder in the ArcGIS Desktop installation folder. There is a file named geographic_transformations.pdf, here you can find ArcGIS 10.1 Geographic and Vertical Transformation Tables.

  • 1
    C:\Program Files (x86)\ArcGIS\Desktop10.1\Documentation\geographic_transformations.pdf
    – ccn
    Apr 4, 2013 at 3:35

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