[Taxacom] Data quality of aggregated datasets
quentin.groom at br.fgov.be
Tue May 7 02:26:58 CDT 2013
This is the problem I've always had with the point-radius method. It
encourages people to document a very precise coordinate and then account
for the error in the radius. The error should be obvious from the number
of decimal places you write, just like any other measurement. The radius
to me is completely irrelevant, there are no statistical methods to use
this information and it doesn't even help you find the original
collection site. In ecological surveys the areas are gridded and the
error is defined by the size of the grid squares. When modelling
distributions, all the current methods uses gridded data and ignore
error radii. When georeferencing legacy material it can be difficult to
assign a location to one grid square or another, however, we are fooling
ourselves if we think the point-radius method is more accurate.
Stephen Thorpe wrote:
> Yes, there is a tendency for biologists to use too many decimal places. Suppose you collect a specimen of a flying insect. How far could it range in 1 day?? Quite far, I think! How did it get to where you found it? Did it travel on you unnoticed for a while and then hop off, only to be captured? Who knows? There is actually no problem with giving an (overly) precise georef. The problem is with interpretation. What does a map of such points plotted mean? It depends on a lot of things. The more points the better, to see the broad patterns. Is it a species of high or low dispersal ability? Does it venture into synanthropic habitats? All these factors can make a difference. Collection localities have fuzzy boundaries. They are not simply "points". Rather they are areas radiating out from a point with ever decreasing probability the further away from the point. But nevermind, let's just get on with it ...
> From: Robert Mesibov <mesibov at southcom.com.au>
> To: dyanega at ucr.edu
> Cc: TAXACOM <taxacom at mailman.nhm.ku.edu>
> Sent: Tuesday, 7 May 2013 5:56 PM
> Subject: Re: [Taxacom] Data quality of aggregated datasets
> Doug Yanega wrote:
> "That means that legacy material being georeferenced NOW is almost all being given coordinates based on a resource like Google Earth, /which uses WGS 84/."
> Collectors are using Google Earth more and more to georeference their sites. Expect to see lots of published or databased lat/lon data like
> with one-hundredth-of-a-second accuracy, because that's the default for cursor position in Google Earth. In my part of the world, that's about +/- 15 cm on the ground.
> I've just checked, and the Australian Bureau of Meteorology says the current temperature in Melbourne, which sprawls over ca 9000 sq. km, is 18.7 C.
> It's the triumph of the 'The More Numbers, The More Scientific' school of thought. I'm glad I've lived to see it. For the curious, I'm 24532.376 days old.
Dr. Quentin Groom
(Botany and Information Technology)
National Botanic Garden of Belgium
Domein van Bouchout
Landline; +32 (0) 226 009 20 ext. 364
FAX: +32 (0) 226 009 45
E-mail: quentin.groom at br.fgov.be
Skype name: qgroom
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