1. Point Radius Method Uncertainty and Best Practices

2. Best Practices Resources MaNIS/HerpNET/ORNIS Georeferencing Guidelines http://manisnet.org/GeorefGuide.html Guide to Best Practices in Georeferencing http://www.gbif.org/participation/training/resources/gbif- training-manuals (http://www.gbif.org/orc/?doc_id=1288h)http://www.gbif.org/orc/?doc_id=1288h

3. Sources of uncertainty:  Coordinate Uncertainty  Map scale  The extent of the locality  GPS accuracy  Unknown datum  Imprecision in direction measurements  Imprecision in distance measurements (1km vs. 1.1km) 20° 30’ N 112° 36’ W ScaleUncertainty (ft)Uncertainty (m) 1:1,2003.3 ft1.0 m 1:2,4006.7 ft2.0 m 1:4,80013.3 ft 4.1 m 1:10,00027.8 ft8.5 m 1:12,00033.3 ft10.2 m 1:24,00040.0 ft 12.2 m 1:25,00041.8 ft12.8 m 1:63,360106 ft32.2 m 1:100,000167 ft50.9 m 1:250,000417 ft127 m

4. Determining uncertainties Precision vs. accuracy Extent of locality GPS accuracy Unknown datum Imprecision in distance measurements Imprecision in coordinate measurements Map scale Imprecision of direction measurements

5. Precision vs. Accuracy Disambiguated Precision is… …the level of detail contained in or described by the data. Example: 42, precise 42.1, more precise 42.01, even more precise Precision can help to minimize uncertainty. More Precise Less Precise

6. Precision vs. Accuracy Disambiguated Accuracy is… …a measure of how close a given value is to the true value.* *We may never actually know the true value in georeferencing, but we do our best to reproduce the location of the true location. Example: Truth = 42 41.999 = more precise, less accurate More Accurate Less Accurate x

7. Precision vs. Accuracy Disambiguated Final Answer? The sum of what we know… about what we don’t know… is the uncertainty.

8. The Extent of the Locality

9. The Extent of the Locality over Time Yellow polygon from GEOLocate

10. GPS Accuracy 5m 9m

11. Unknown Datum Error assuming NAD27 vs. NAD83 or WGS84

12. Imprecision in Distance Measurements

13. Imprecision in Coordinate Measurements 20° 30’ N 112° 36’ W vs. 20° 30’ N 112° 30’ W Uncertainty based on coordinate precision using the WGS84 reference ellipsoid

14. Map Scale USGS Standard: "For maps on publication scales larger than 1:20,000, not more than 10 percent of the points tested shall be in error by more than 1/30 inch, measured on the publication scale; for maps on publication scales of 1:20,000 or smaller, 1/50 inch." USGS Map Accuracy 1/30th (.033) inch 1/50th (.02) inch

15. Imprecision of Direction Measurements Error: N > NE > ENE