The default Coordinate System assigned to georeferenced data

Question

Unless I'm mistaken, it appears that the default coordinate system assigned to my georeferenced data is the Map's coordinate system.

I suppose I'm OK with that, and I can change it if I want, but my question is:

"Why is the default NOT the Target data coordinate system that I'm matching to?"

That seems more "logical" to me, but I must be wrong, so I'm wondering if anyone can explain WHY it's the Map coordinate system, instead?

Thanks, CCE

LizAbbey · Answer

@Craig_Eissler_Iceman This is for your college students:

There is no step in the georeferencing workflow to nominate a "Target" dataset. You simply start georeferencing by adding in control points. There isn't even a requirement to have a target dataset. The software does not know how you are determining the control points for georeferencing.

The software does know the coordinate system of the space you are georeferencing into, which is the coordinate system of the map frame. As a result, you get an output in the same coordinate system as the map frame.

RTPL_AU · Answer

@Craig_Eissler_Iceman 
My process is to assign the coordinate system to non-georeferenced CAD or raster data in Catalog before I add it to a map/project. 
I then make sure there is at least one known layer in a map, and that the map is in the correct coordinate system, with the correct transformations applied, before I add the raster layer into the map and start the georeferencing process.

This way I always know what is going on and have visual cues with other data to see if things are going south (pun sort of intended) while working on the georeferencing. 
With the various automatic 'things' that Pro do to 'help' users, I prefer to georeference this way, and in this sequence, even if some docs describe other processes working fine.

Edit:
The Book of Why will be a captivating read if ever published.

danretired · Answer

Just tell them...

- to an empty map, add your Target layer  ( no basemap, no specified coordinate system if it differs from Target)

- This will set the coordinate system of the map and will assure that the output coordinate system will be preserved and equal to the input, in case you forget to set or check your inputs or outputs

- of course, .... always check, never assume, always set ... is the first step in doing anything (you reference your lecture date here 😁 )