Dear Dan

> I found the list on the CF web site here:
> http://cfconventions.org/Data/cf-standard-names/docs/area-type-table.html

You probably saw John Graybeal's posting that he has put the up-to-date
list at http://mmisw.org/ont/cf/areatype.

> The only references to area_type in the CF conventions doc (v1.6) appear to 
> be in section 7.3.3 Statistics applying to portions of cells. However our 
> data are point values (obtained by interpolating point observations) so we 
> are not defining bounds for the spatial coordinates and therefore do not have 
> a cell method for 'area'. Is it still possible to use area_type as a 
> coordinate variable in this situation?

Yes. It has a special role in that section, but it is always permissible to
attach coordinate variables to quantities to describe the data variable, and
the area_type is often needed for such a purpose.

> x=180
> y=290
> time=UNLIMITED
> ntypes=1
> maxlen=20
> 
> lat(y,x)
> lon(y,x)
> 
> surface_type(ntypes,maxlen)
> surface_type:standard_name="area_type"
> surface_type="grass"
> 
> surface_temperature(time,ntypes,y,x)
> surface_temperature:coordinates = "lat lon surface_type"
> surface_temperature:cell_methods = "time: minimum within days   time: mean 
> over days"

> Personally I'm not that keen on having to add a dimension

You don't have to add a dimension. You can use a scalar coord var, thus:

> x=180
> y=290
> time=UNLIMITED
> maxlen=20
> 
> lat(y,x)
> lon(y,x)
> 
> surface_type(maxlen)
> surface_type:standard_name="area_type"
> surface_type="grass"
> 
> surface_temperature(time,y,x)
> surface_temperature:coordinates = "lat lon surface_type"
> surface_temperature:cell_methods = "time: minimum within days   time: mean 
> over days"

This might be a good subject for the FAQ because it has come up before.

Best wishes

Jonathan
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