![Page 1: Point Radius Method Uncertainty and Best Practices](https://reader035.vdocument.in/reader035/viewer/2022062422/56649f135503460f94c26d77/html5/thumbnails/1.jpg)
Point Radius Method
Uncertainty and Best Practices
![Page 2: Point Radius Method Uncertainty and Best Practices](https://reader035.vdocument.in/reader035/viewer/2022062422/56649f135503460f94c26d77/html5/thumbnails/2.jpg)
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)
![Page 3: Point Radius Method Uncertainty and Best Practices](https://reader035.vdocument.in/reader035/viewer/2022062422/56649f135503460f94c26d77/html5/thumbnails/3.jpg)
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’ WScale Uncertainty (ft) Uncertainty (m)
1:1,200 3.3 ft 1.0 m
1:2,400 6.7 ft 2.0 m
1:4,800 13.3 ft 4.1 m
1:10,000 27.8 ft 8.5 m
1:12,000 33.3 ft 10.2 m
1:24,000 40.0 ft 12.2 m
1:25,000 41.8 ft 12.8 m
1:63,360 106 ft 32.2 m
1:100,000 167 ft 50.9 m
1:250,000 417 ft 127 m
![Page 4: Point Radius Method Uncertainty and Best Practices](https://reader035.vdocument.in/reader035/viewer/2022062422/56649f135503460f94c26d77/html5/thumbnails/4.jpg)
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
![Page 5: Point Radius Method Uncertainty and Best Practices](https://reader035.vdocument.in/reader035/viewer/2022062422/56649f135503460f94c26d77/html5/thumbnails/5.jpg)
Precision vs. AccuracyDisambiguated
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
![Page 6: Point Radius Method Uncertainty and Best Practices](https://reader035.vdocument.in/reader035/viewer/2022062422/56649f135503460f94c26d77/html5/thumbnails/6.jpg)
Precision vs. AccuracyDisambiguated
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
![Page 7: Point Radius Method Uncertainty and Best Practices](https://reader035.vdocument.in/reader035/viewer/2022062422/56649f135503460f94c26d77/html5/thumbnails/7.jpg)
Precision vs. AccuracyDisambiguated
Final Answer?
The sum of what we know…
about what we don’t know…
is the uncertainty.
![Page 8: Point Radius Method Uncertainty and Best Practices](https://reader035.vdocument.in/reader035/viewer/2022062422/56649f135503460f94c26d77/html5/thumbnails/8.jpg)
The Extent of the Locality
![Page 9: Point Radius Method Uncertainty and Best Practices](https://reader035.vdocument.in/reader035/viewer/2022062422/56649f135503460f94c26d77/html5/thumbnails/9.jpg)
The Extent of the Locality over Time
Yellow polygon from GEOLocate
![Page 10: Point Radius Method Uncertainty and Best Practices](https://reader035.vdocument.in/reader035/viewer/2022062422/56649f135503460f94c26d77/html5/thumbnails/10.jpg)
GPS Accuracy
5m
9m
![Page 11: Point Radius Method Uncertainty and Best Practices](https://reader035.vdocument.in/reader035/viewer/2022062422/56649f135503460f94c26d77/html5/thumbnails/11.jpg)
Unknown Datum
Error assuming NAD27 vs. NAD83 or WGS84
![Page 12: Point Radius Method Uncertainty and Best Practices](https://reader035.vdocument.in/reader035/viewer/2022062422/56649f135503460f94c26d77/html5/thumbnails/12.jpg)
Imprecision in Distance Measurements
![Page 13: Point Radius Method Uncertainty and Best Practices](https://reader035.vdocument.in/reader035/viewer/2022062422/56649f135503460f94c26d77/html5/thumbnails/13.jpg)
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
![Page 14: Point Radius Method Uncertainty and Best Practices](https://reader035.vdocument.in/reader035/viewer/2022062422/56649f135503460f94c26d77/html5/thumbnails/14.jpg)
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
![Page 15: Point Radius Method Uncertainty and Best Practices](https://reader035.vdocument.in/reader035/viewer/2022062422/56649f135503460f94c26d77/html5/thumbnails/15.jpg)
Imprecision of Direction Measurements
Error: N > NE > ENE