[Taxacom] Inappropriate accuracy of locality data

Frederick W. Schueler bckcdb at istar.ca
Fri Dec 3 15:59:40 CST 2010

On 12/3/2010 4:03 PM, Bob Mesibov wrote:

> Most contributors to this discussion agree that positions should be reported together with an explicit uncertainty. Under ideal conditions for the eTrex, you would report your single measurement as 41 52 38.84 N, 87 39 08.48 W +/- 15 m. (You could also report the uncertainty in seconds, but the longitude error increases dramatically with latitude.) Normally, however, you don't know whether the measurement was or was not under ideal conditions, so that uncertainty is a guess.

* I'm dealing with some datasheets now where UTM was reported to 0.1mm. 
Fortunately, there was also an "extent of site" field on the sheet, so 
this doesn't have to stand as an implied accuracy.

> You can improve on the uncertainty by taking multiple readings at the same point, and *averaging* them and reporting the variation in the sample. Dusty, I hate to say this, but that average position might be different from all the individual readings - it could be an *entirely new point*! OMG! It might not even be an improvement, because there could be a systematic bias in the GPS reading, and the average might be further from the true position than your first, single reading.

* I've done this with the Garmin 45, in our driveway, and found that the 
reported error was similar to the standard deviation of the sample.

fred schueler
          Frederick W. Schueler & Aleta Karstad
Bishops Mills Natural History Centre - http://pinicola.ca/bmnhc.htm
now in the field on the Thirty Years Later Expedition -
Daily Paintings - http://karstaddailypaintings.blogspot.com/
     RR#2 Bishops Mills, Ontario, Canada K0G 1T0
   on the Smiths Falls Limestone Plain 44* 52'N 75* 42'W
    (613)258-3107 <bckcdb at istar.ca> http://pinicola.ca/

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