[Taxacom] Data quality of aggregated datasets

Robert Mesibov mesibov at southcom.com.au
Tue May 7 04:19:36 CDT 2013


Quentin Groom wrote:

"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."

I think that depends on how you understand the point-radius method. The idea is that there's a circle which completely contains the area searched or sampled. The point is simply an estimate of that circle's centre, and is not meant to be an estimate of the location of the actual collecting site (assuming there was just one) plus a measurement error. The point+radius define a circular *area* containing the collecting site in an easily understandable way.

How many decimal places you use for the point's location should obviously (to me, anyway) depend on the magnitude of the radius. Recording 22°06'57.54"S
117°53'15.31"E +/- 100 m is, I think, bizarre. [We've had a discussion about this on Taxacom before, and some listers think that rounding off is throwing away data.]

You can also define a collecting *area* by the implied uncertainty in a single point estimate, as you suggest. However, I don't think many people on this list would know the uncertainty at a glance in 22.116°S 117.888°E. A computer can pull it out, but eyeballing the area in a point-radius record is easier.

Another difficulty with implied uncertainty occurs with the above-mentioned computer when UTM data are converted to lat/lon, or vice-versa, or for that matter with lat/lon format conversions. In my audit paper in ZooKeys I cite a wonderful GBIF/ALA example where '12 km SE of Millaa Millaa' (Queensland, 1971) got processed from 17°36'S 145°42'E to -17.6000003814697 145.699996948242. Implied uncertainty of a few atomic radii, maybe?
-- 
Dr Robert Mesibov
Honorary Research Associate
Queen Victoria Museum and Art Gallery, and
School of Agricultural Science, University of Tasmania
Home contact: PO Box 101, Penguin, Tasmania, Australia 7316
Ph: (03) 64371195; 61 3 64371195




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