Dear Martin I'd rather we retained "fraction" in the standard name, because it's always been there, it's used in other contexts in a consistent way, and there isn't anything actually incorrect with it, as you say. Could we instead add a note to the definitions pointing out that percent is acceptable as a unit for them?
Best wishes Jonathan ----- Forwarded message from Martin Juckes - UKRI STFC <[email protected]> ----- > Date: Wed, 30 Jan 2019 22:40:12 +0000 > From: Martin Juckes - UKRI STFC <[email protected]> > To: Steven Emmerson <[email protected]> > Cc: "CF-metadata ([email protected])" <[email protected]> > Subject: Re: [CF-metadata] Putting the units in a CF standard name: > area_fraction > > Hi Steve, > > > The issue is more that CF allows more freedom in the choice of units than > many people expect from a "fraction". > > > A second problem, I think the problem is that I didn't explain the issue > clearly. In the CMIP data request we are specifying that variables with > standard name "area_fraction" should be given as percentages. This is allowed > by the CF convention: an "area_fraction" can be 0.5 or 50%. The reason that > percentages are being used is because "area_fraction" is being used like the > proportion of land covered in grass, and people are used to having these as > percentages rather than fractions. It is all perfectly correct as far as the > convention goes, but people often interpret the use of "area_fraction" for a > percentage as an error. > > > Given that we have the framework of allowing flexibility in the choice of > units, I feel it would be better to avoid having the term "fraction" in the > standard name, given that it is often interpreted as implying a specific > choice for the units. > > > regards, > > Martin > > > ________________________________ > From: Steven Emmerson <[email protected]> > Sent: 30 January 2019 21:37 > To: Juckes, Martin (STFC,RAL,RALSP) > Cc: CF-metadata ([email protected]) > Subject: Re: [CF-metadata] Putting the units in a CF standard name: > area_fraction > > On Wed, Jan 30, 2019 at 12:54 PM Martin Juckes - UKRI STFC > <[email protected]<mailto:[email protected]>> wrote: > > I'm afraid I don't understand your comment. When I search for "fraction" in > the NIST document I find it defined as being a ratio, which is inconsistent > with the current CF usage. The CF standard name concept "area_fraction" is > not what NIST or others understand as a "fraction". I'm suggesting a change > to remove this inconsistency. > > Unless we're talking past one another, I'll have to disagree. The NIST unit > for "mass fraction" is "1" -- even though it's a ratio. A fraction can be > represented many ways. "1:2", "1/2", and "0.5" all represent the same > fraction, for example. > > Does the CF convention require a particular representation for a fraction? > > Regards, > Steve Emmerson > _______________________________________________ > CF-metadata mailing list > [email protected] > http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata ----- End forwarded message ----- _______________________________________________ CF-metadata mailing list [email protected] http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
