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I need to transform some data from PSA56 to NAD83. It doesn't have to be that rigorous as it's purely for a context map. I'm guessing I will need to go to WGS84 and then to NAD83. If anyone has any suggestions for best practice please let me know. Using ArcGIS10

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Many transformations are location-based, so giving a general location is useful. Check EPSG registry,, for possibilities and/or the geographic_transformations.pdf file in your install, documentation folder. – mkennedy Sep 15 '13 at 22:13
up vote 1 down vote accepted

You are trying to impose a North American Datum on South America data which does not work.

PSAD stands for Provisional South American Datum developed in 1956.

I would highly recommend you convert it to WGS 84 and assign the UTM zone if you have to do it for a particular country, region etc. This should resolve your issue.

If you do not know which UTM Zone you have to apply refer to this link which could be helpful.

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