Dear @JimBiardCics

I appreciate the point and I agree that we should not spend our time doing a 
less good job of something which is already available elsewhere. However I 
don't think that CF is fairly described as "reinventing the wheel" in this 
case. I can suggest a few reasons why we have our own set of `grid_mapping` 
definitions rather than relying on `proj4` for example.

* An external resource might not include all the cases we need. Does `proj4` 
include rotated pole and vertical perspective, for instance? (If it does that 
is not noted in our App F). If it's not our own resource, we can't necessarily 
add to it, and if it's not comprehensive, users of CF might have to mix 
different conventions in their files, which would be less satisfactory.

* An external resource might change in a way which didn't suit CF, meaning we'd 
have to do extra work in a hurry to replace it with something else, with the 
further penalty of backwards-incompatibility for CF.

* An external resource might not present the information in a way which is 
easily usable in CF, because it's not organised in a similar fashion or doesn't 
match well to the CF data model.

Therefore instead of "handing over" something to an external authority, I feel 
that in most cases it is better to import the external information to CF. This 
isn't an absolute rule, of course, but it seems fine for `grid_mapping` to me. 
However, your point is a good reason why we should make the choice of 
attributes as similar as we can to `proj4`. If we do that, it should be easy to 
import more of them, like new standard names on existing patterns, and it 
improves interoperability between conventions. If we find there is a use case 
which is *not* trivial to import, there's probably a good reason for that which 
will require some thought, like new standard names which propose new patterns.

Best wishes

Jonathan


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