Dear Mark area_type is given in the standard_name table as having a unit of 1. It is a categorical string-valued quantity.
Sect 3.1 of CF 1.6 says "Units are not required for dimensionless quantities. A variable with no units attribute is assumed to be dimensionless. However, a units attribute specifying a dimensionless unit may optionally be included." So, putting units="1" or omitting the units both mean the quantity is dimensionless. Best wishes Jonathan ----- Forwarded message from "Hedley, Mark" <mark.hed...@metoffice.gov.uk> ----- > Date: Thu, 30 Oct 2014 08:37:14 +0000 > From: "Hedley, Mark" <mark.hed...@metoffice.gov.uk> > To: "cf-metadata@cgd.ucar.edu" <cf-metadata@cgd.ucar.edu> > Subject: Re: [CF-metadata] string valued coordinates > > Hello CF > > > From: CF-metadata [cf-metadata-boun...@cgd.ucar.edu] on behalf of Jonathan > > Gregory [j.m.greg...@reading.ac.uk] > > > Yes, there are some standard names which imply string values, as Karl says. > > If the standard_name table says 1, that means the quantity is > > dimensionless, so it's also fine to omit the units, as Jim says. > > I would like to raise question about this statement. Omitting the units and > stating that the units are '1' are two very different things; > dimensionless != no_unit > is an important statement which should be clear to data consumers and > producers. > > If the standard name table defines a canonical unit for a standard_name of > '1' then I expect this quantity to be dimensionless, with a unit of '1' or > some multiple there of. > If the standard name states that the canonical unit for a standard_name is '' > then I expect that quantity to have no unit stated. > Any deviation from this behaviour is a break with the conventions. I have > code which explicitly checks this for data sets. > > Are people aware of examples of the pattern of use described by Jonathan, > such as a categorical quantities identified by a standard_name with a > canonical unit of '1'? > > thank you > mark > _______________________________________________ > CF-metadata mailing list > CF-metadata@cgd.ucar.edu > http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata ----- End forwarded message ----- _______________________________________________ CF-metadata mailing list CF-metadata@cgd.ucar.edu http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
