[CF-metadata] [CF Metadata] #8: Identifying horizontal coordinate variables using the axis attribute

[Jonathan Gregory]

Dear Dominic

> but I've just read the archive and I am very interested as to why this 
> discussion has been limited to identifying only horizontal coordinate 
> variables, and does not include the identification of vertical coordinate 
> variables (Z). 

It hasn't been limited. As you would wish, the axis attribute can be used to
indicate vertical (Z) and time (T) axes as well as horizontal (X and Y). The
ticket was about horizontal axes only because there was some confusion about
what they meant in the case when they are not long and lat.

The axis attribute is not required (just recommended) for backward-
compatibility with COARDS, which specified other ways to identify axes.

Best wishes

Jonathan