[Taxacom] Geodetic datums do matter

Derek Sikes ffdss at uaf.edu
Mon Mar 23 18:24:26 CDT 2009

As much as I agree with Doug's general points and the exceptions  
pointed out by others, I'm working in the Aleutians and this region in  
North America has large errors associated with unknown datum (>400 m  
in some cases):


And these MaNIS/HerpNet/ORNIS georeferencing guidelines indicate an  
error of 1km is to be used for areas outside those already determined.

My point: the error of unknown datum can be larger than 200m and there  
is no difficulty in recording it in the field & corresponding  
database, so why fail to do so?

But again, I agree with Doug that for most cases it will be  
unimportant (but why not still record it?). I would argue, however,  
that its importance is too small to justify the space it would take on  
an insect label.


On Mar 23, 09, at 2:47 PM Mar 23, 09, Doug Yanega wrote:

> Fred Schueler wrote:
>> * I don't know: certainly there are many situations where 200m  
>> doesn't
>> matter, but there have been many times when a GPS has led me to the  
>> spot
>> where a single specimen of a nearly-sessile snail was taken by a
>> deceased colleague, or from which declining frogs had been heard
>> calling, or where a particular rare plant had been discovered, or a
>> colony of an invasive plant had been found. In these cases a 200m  
>> error
>> or uncertainty would have ruined the replication I was trying to
>> achieve. [snip]
>> For herpetology, malacology, and invasive plants, I'd say that 10m of
>> error is acceptable, but not much more.
> Karl Magnacca wrote:
>> I agree for many cases in entomology as well; 20m accuracy isn't  
>> great,
>> but the difference between 20m and 200m error is between being able  
>> to
>> eyeball the location of a particular patch of plants from the  
>> point, and
>> blundering around in dense forest for hours trying to find it.
> and Erast Parmasto wrote:
>> In Estonia,
>> we have on collecting labels the data of some very rare fungal  
>> species
>> with coordinates determined using older types of GPS up to ten years
>> ago already. Now these species are protected by law in this country,
>> and it is really important where a locality is actually situated.  
>> In a
>> small forest of one owner of the land plot, or in a neighbouring
> forest owned by another man.
> I would have hoped it was clear that I was not implying that you or I
> couldn't come up with dozens of scenarios where precision is
> important - but rare plants, rare fungi, rare sessile snails, and
> invasive plants that only occur in a SINGLE PATCH, are all *extremely
> exceptional* cases. There are not going to be very many species on
> this planet that will be found ONLY in an area that is less than 50m
> in diameter, never straying beyond that boundary. Just because there
> are exceptional cases doesn't invalidate the existence of a general
> pattern, and the general pattern is that if you give a biologist a
> GPS reading and let them go in search of an organism, even a 200m
> error is almost never - *in and of itself* - going to make it
> impossible for them to find what they're after, because most
> organisms don't occur as isolated individuals or "particular patches"
> that could never be found unless you go back to the exact square
> meter they were first seen (and most biologists wouldn't give up
> looking after searching only a 20m radius). Certainly, if you happen
> to work on organisms that *are* in that exceptional category, then by
> all means you should take all necessary steps to record your
> geolocations as precisely as possible, but for the vast majority of
> cases, that level of precision is meaningless.
> Peace,
> -- 
> Doug Yanega        Dept. of Entomology         Entomology Research  
> Museum
> Univ. of California, Riverside, CA 92521-0314        skype: dyanega
> phone: (951) 827-4315 (standard disclaimer: opinions are mine, not  
> UCR's)
>              http://cache.ucr.edu/~heraty/yanega.html
>   "There are some enterprises in which a careful disorderliness
>         is the true method" - Herman Melville, Moby Dick, Chap. 82
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Derek S. Sikes, Curator of Insects
Assistant Professor of Entomology
University of Alaska Museum
907 Yukon Drive
Fairbanks, AK   99775-6960

dsikes at alaska.edu

phone: 907-474-6278
FAX: 907-474-5469

"Remember that Truth alone is the matter you are in Search after; and  
if you have been mistaken, let no Vanity reduce you to persist in your  
mistake." Henry Baker, London, 1785

University of Alaska Museum of the North -

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