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If I have a shapefile in ArcMap and I go to export it, the export data dialog comes up with a mandatory choice of using the layer's data source coordinate system or the data frame's coordinate system.

I was interested if someone can explain to me what both of these are in most simple terms.

I will write down what I thought they were and please do correct me.

If I have a shapefile that is in WGS 1984 and I export it with the layer's data source option it will retain the WGS 1984 co-ordinates.

If I were to pick to use the data frame option, which in European 1950, it will give it the data frame co-ordinates. But the actual conversion has not been done.

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ArcGIS projection on the fly is active when the "data" is not in the same coordinate system than the "data frame". However, you should be aware that the datum transformation is not automatically selected by ArcGIS (you should get an ArcGIS warning if different datums are used. When you use "export data" and select "same as dataframe", ArcGIS will use the same parameters as it is using "on the fly". As a result, your output coordinate system will be ED 1950 BUT this will be wrong coordinates because of the absence of transformation.

In summary, export data "same as dataframe" applies the same parameter than the "on the fly" projection.

To solve your problem, select the transformation from "data frame" properties > enter image description here

See page 13 (primarily) on this page to select the best transformation in your case

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  • Hi there , so if you have your data transformation set up correctly then picking the use the data frame will essentially do the conversions on the fly ? Sep 7, 2015 at 16:01
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    @JackWalker Yes. It's worth reinforcing that if you have added WGS84 data to a ED1950 dataframe but not specified a transformation, it's not being displayed in the proper location or correctly worked with if you're running any GP tools on it, never mind exporting it. If you're simply adding the layer to the dataframe in order to reproject it and then save the result, 1) you still need to specify the transformation when adding and 2) there is a Project tool specifically for that purpose, no dataframe manipulation required (still have to specify transformation).
    – Chris W
    Sep 7, 2015 at 18:50

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