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When opening an edit session Arc is telling me that some of my shape files' coordinate systems do not match the data frame.

Here is the data frame coordinate system:

Stereo_70

Projection: Double_Stereographic

False_Easting: 500000.000000

False_Northing: 500000.000000

Central_Meridian: 25.000000

Scale_Factor: 0.999750

Latitude_Of_Origin: 46.000000

Linear Unit: Meter

GCS_Dealul_Piscului_1970

Datum: D_Dealul_Piscului_1970

And here is the coordinate system that all the shape files in question have:

Projected Coordinate System: Stereo_70

Projection: Double_Stereographic

False_Easting: 500000.00000000

False_Northing: 500000.00000000

Longitude_Of_Origin: 25.00000000

Scale_Factor: 0.99975000

Latitude_Of_Origin: 46.00000000

Linear Unit: Meter

Geographic Coordinate System: GCS_Dealul_Piscului_1970

Datum: D_Dealul_Piscului_1970

Prime Meridian: Greenwich

Angular Unit: Degree

Now is it just me or is anyone else having difficulty seeing the difference? Doe this mean I'm going to have to reproject the files in question FROM their original projection, TO their original projection? I'm not even sure that's possible but will try now.

And short of that I guess I just wipe the projections and define them again.

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    ArcMap is terribly stupid in this case. It always looks at the name of the projection, not at the actual parameters. I either ignore this error, or use the define projection tool to define the projection of all layers to one projection. – Devdatta Tengshe May 23 '13 at 8:04
  • Thanks Devdatta. I don't mind if it points out that I forgot to project something. That's quite useful. But this is... well... rubbish :) I shall define away. Thanks again. – Oliver Burdekin May 23 '13 at 8:06
  • I've often faced this problem when data comes from other software. That software might use the correct parameters for say UTM 43N, but the name is not what ArcGIS expects. And all ArcMap can do, it to throw this Warning. – Devdatta Tengshe May 23 '13 at 8:08
  • @DevdattaTengshe could you add this as an answer? I agree it is quite terrible, and one would not be inclined to think that something so simple is the cause. – Cindy Jayakumar May 23 '13 at 8:08
  • Slightly less rigorous but quicker than "define projection" I think, I just went into catalog, selected the properties for the shapefiles and altered (well, not altered at all really) the projections there. Editor is now satisfied in ArcMap. Nothing like making a workflow easier. – Oliver Burdekin May 23 '13 at 8:15
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One of the strange Limitations of ArcMap, is that it only looks at the name of the projection, and doesn't actually check the parameters, if the name is different.

I've often faced this problem when data comes from other software. That software might use the correct parameters for say UTM 43N, but the name is not what ArcGIS expects. And all ArcMap can do, it to throw this Warning.

In this case you have two options, both equally good:

  • Just ignore the warning.
  • Use the Define Projection tool, and set the projection of the problematic layer to the projection that ArcGIS expects. (Note: that I am talking about the Define Projection tool, and not the Project tool). This tool will just reset the coordinate system, and will not touch the coordinates. This option might involve more work, but you won't face the warning again in the future.

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