NAD 1927 to NAD 1983 Feature classes/Shapefiles do not line up.

12-06-2011 06:41 AM
New Contributor
I have accumulated several feature classes and shapefiles that have been created from exported  GPS/Trimble software .cor files using the NAD 1927 UTM Zone 18N coordinate system. All my GPS files and geodatabases use this system. I am now trying to convert all of this over to the NAD 1983 UTM Zone 18N coordinate system. Here is what I am running into: When I add a shapefile to a data frame in ArcMap-ArcInfo that has been GPS'd and exported via Pathfinder Office using the NAD 1983 system and then add a feature class that has a 1927 coordinate system (using the NAD 1927 to NAD 1983 NADCON transformation), the items line up fine. If I use ArcCatalog to clear the coordinate system of a feature class with a 1927 system and then change the coordinate system of that feature classes to the 1983 system, the feature class with the changed system (1927 to 1983) does not properly line up in the ArcMap data frame with the  shapefile that was originally GPS'd and exported via Pathfinder Office using the NAD 1983 system.

If more details are needed, I will gladly clarify.

Am I missing something?

Thanks in advance.
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Esri Notable Contributor
Hi James,

Yes, what you're seeing is correct. When you change the coordinate system in ArcCatalog via the data's property page, or with the Define Projection Tool in ArcToolbox, only the metadata is updated. The coordinate values themselves are unchanged. So you have NAD83-labeled that is still georeferenced to NAD27. Use the Project Tool instead to create data that is on NAD83.

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New Contributor
Hi Melita,

     Thank you very much for the information. It made me realize that I was not using the "project" and "define projection" tools properly. I was not using the tools in the correct order, nor was I looking closely enough at the coordinate system (or lack thereof) of the shapefiles, feature classes, or feature datasets I was working with.

Jim R.
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