Martin, I like your definition.
While there is a case for renaming the standard name, it’s long-time use, validity, and the fact only sophisticated data managers use standard names (and most data users just look primarily at variable names) says to me we should keep the existing standard names with fraction. John > On Jan 31, 2019, at 08:07, Jim Biard <jbi...@cicsnc.org> wrote: > > Hi. > > I understand that concern, but it has always been true that the units for a > quantity identified by a standard name only has to be convertible using > UDUNITS from the canonical units specified in the definition for that > standard name. So percent is, by definition, valid for a quantity with units > of '1'. As you can see below: > > > udunits2 > You have: 1 > You want: percent > 1 = 100 percent > x/percent = 100*(x/) > > I guess I don't see the need for guidance here. > > Grace and peace, > > Jim > >> On 1/31/19 10:51 AM, Martin Juckes - UKRI STFC wrote: >> Dear Jonathan, >> >> >> we could certainly take that approach, though the definitions are not always >> accessible to people looking at the standard name, so they do not compensate >> for ambiguity in the name itself. >> >> >> The current text '"Area fraction" means the fraction of horizontal area.' >> could be replaced with >> >> >> "Area Fraction" is a dimensionless number representing a relative or >> proportional area. It may be expressed as a fraction, percentage or any >> other unit that conforms to "1". It is evaluated as the area of interest >> divided by the grid cell area, scaled for the units chosen. >> >> >> I still feel that there is a case for changing the name to, for example, >> "relative_area" in order to reduce confusion caused by people who assume >> that a fraction is a quantity that does not have units, >> >> >> regards, >> >> Martin >> >> >> >> >> ________________________________ >> From: CF-metadata <cf-metadata-boun...@cgd.ucar.edu> on behalf of Jonathan >> Gregory <j.m.greg...@reading.ac.uk> >> Sent: 31 January 2019 13:20:24 >> To: cf-metadata@cgd.ucar.edu >> Subject: [CF-metadata] Putting the units in a CF standard name: area_fraction >> >> 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 >> <martin.juc...@stfc.ac.uk> ----- >> >>> Date: Wed, 30 Jan 2019 22:40:12 +0000 >>> From: Martin Juckes - UKRI STFC <martin.juc...@stfc.ac.uk> >>> To: Steven Emmerson <emmer...@ucar.edu> >>> Cc: "CF-metadata (cf-metadata@cgd.ucar.edu)" <cf-metadata@cgd.ucar.edu> >>> 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 <emmer...@ucar.edu> >>> Sent: 30 January 2019 21:37 >>> To: Juckes, Martin (STFC,RAL,RALSP) >>> Cc: CF-metadata (cf-metadata@cgd.ucar.edu) >>> 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 >>> <martin.juc...@stfc.ac.uk<mailto:martin.juc...@stfc.ac.uk>> 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 >>> 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 >> _______________________________________________ >> CF-metadata mailing list >> CF-metadata@cgd.ucar.edu >> http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata > -- > Visit us on > Facebook Jim Biard > Research Scholar > Cooperative Institute for Climate and Satellites NC > North Carolina State University > NOAA National Centers for Environmental Information > formerly NOAA’s National Climatic Data Center > 151 Patton Ave, Asheville, NC 28801 > e: jbi...@cicsnc.org > o: +1 828 271 4900 > > Connect with us on Facebook for climate and ocean and geophysics information, > and follow us on Twitter at @NOAANCEIclimate and @NOAANCEIocngeo. > > _______________________________________________ > CF-metadata mailing list > CF-metadata@cgd.ucar.edu > http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
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