Dear Jim

Thanks for the example. Before the `string` data type was introduced, you would 
have used `char front_type_name(front_type,stringmaxlength)`. Since it's an 
auxiliary coordinate variable, it is recommended not to give it the same name 
as its dimension (in chapter 5). My interpretation is that it's still an 
auxiliary coordinate variable when string-valued, though now 1D, and therefore 
should not have the same name as its dimension. I don't think it can be a 
dimension coordinate variable because it's not numeric, and Section 1.2 says 
[dimension] coordinate variables must be numeric. I think I'm correctly stating 
the convention as it stands. Maybe the word "should" is the problem in how I 
stated it. :-) In fact it's not an error for you to have `string 
front_type(front_type)` as an auxiliary coordinate variable (named by the 
`coordinates` attribute) but the CF checker should produce a warning, I think.

However, you would like `string front_type` to be a dimension coordinate 
variable (which doesn't have to be named in the `coordinates` attribute). For 
me, that means that the ordering is inherently meaningful, which in turn means 
we have to define a collating sequence as a CF standard, and I'm nervous of 
doing that, because it would be unreliable. I would guess that there is no 
inherent meaning to the order of a list of front types. Is that right? In a 
dimension coordinate variable, the values also have to be unique, but that's 
not difficult to enforce consistently.

If it's an auxiliary coordinate variable, then giving it a different name from 
its dimension is no more problematic than for any other 1D auxiliary coordinate 
variable. You remark that it's not really a problem. The choice is whether 
alleviating this annoyance is worth the cost of the possible confusion of 
having something that looks like a dimension coordinate variable but isn't, 
which is my objection to it.

Best wishes
Jonathan

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