The default Coordinate System assigned to georeferenced data

[Craig_Eissler_Iceman]

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

[DanPatterson]

"By default, a map or scene is assigned the coordinate system of the first feature layer you add to it."

From the help.

If you set a specific default spatial reference to use for all maps then all your data and subsequent processes will use that coordinate system.

In your case, one could not set a specific coordinate system, add your target data first ( no basemap for instance), then the map would be set to it and subsequent activities would use it.

I prefer not to use a basemap, I add my data which is in the spatial reference that I want to use for all subsequent processes and I don't have to worry about it not being used.

I suspect a decision has to be made about what one to use and making the assumption that you want to use the target data coordinate system would not work in some workflows.

[Craig_Eissler_Iceman]

Thanks, though I'm not sure what the 1st layer added to the map or a Basemap has to do with georeferencing. ...Yes, I understand how the Map coordinate system gets set that way, etc.

I was just wondering WHY a georeferenced layer gets assigned the Map's coordinate system rather than the Target layer that you're matching to, which seems more logical to me since that's what you're aligning with. 

Personally, I don't have this issue because, like you, I have everything in the same projected coordinate system, I was just wondering how I might explain this georeferencing-coordinate system assignment behavior to my college students -- especially if there was some sound logic to it.

I'm OK with telling them "I don't know why" the developers had to make a decision and the default they went with was the Map instead of the Target layer.

[DanPatterson]

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 😁 ) 

[RTPL_AU]

@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.

[LizAbbey]

@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.