Georeferencing Collections & Determining Uncertainty

1. Georeferencing Collections& Determining Uncertainty Arthur D. Chapman Australian Biodiversity Information Services

2. http://www.gbif.org/orc/?doc_id=1288 Chapman & Wieczorek (eds) (2006)

3. Introduction • The document provides guidelines to World’s Best Practice for georeferencing, including guidance on • determining a georeference • determining the spatial uncertainty • recording the georeferences and uncertainties • Several earlier projects provided a good starting point • Biogeomancer Classic • MANIS-HerpNet • MapSteDI • Diva-GIS • HISPID • CRIA • ERIN

4. A Best Practices Document provides • Speed and efficiency • Consistency • Training of new data entry operators • Improved data quality • Transparency and documentation • Scrutiny of management and external/internal auditors • Scrutiny of users of the information

5. Principles of Best Practice • Accuracy– a measure of how well the data represent true values. • e.g. represented by an uncertainty radius (or polygon of uncertainty) in georeferencing • Effectiveness – the likelihood that a task achieves its desired objectives. • e.g. the percentage of records for which the latitude and longitude can be accurately determined. • Efficiency – the ratio of output to input. • e.g. the effort that is needed to produce an acceptable output. Also the amount of input data the user has to obtain to produce an acceptable result (e.g. gazetteers, collectors itineraries, etc.) • Reliability – refers to the consistency for which results are produced • e.g. refers to the repeatability for which a georeference can be produced by the user for the same locality.

6. Principles of Best Practice • Accessibilty – how accessible the results are to the users/ public • e.g. the ease with which users and other institutions can access the georeference for a particular locality that has already been georeferenced. • Transparency – an annunciation of the procedures for collection, analysis, reporting and update. • e.g. refers to the transparency of methods used to georeference a particular locality. • Timeliness – relates to the frequency of data collection, its reporting and updates. • e.g. includes update frequency of gazetteers, new methodologies, and when records are georeferenced and made available to others. • Relevance – the data collected should meet the needs of the user – i.e. should fulfill the principle of “fitness for use”. • e.g. refers to the format of the output (does it include Datum etc.) and does it include good metadata on the above topics)

7. Collecting Data in the Field Using a GPS • Accuracy variable (seldom as good as ‘reported’ on the GPS Unit!) • DGPS • Wide Area Augmentation Systems (WAAS) • Local Area Augmentation Systems (LAAS) • Document • Coordinates • Datum • Accuracy reported by GPS

8. Collecting Data in the Field Recording Datums • Different datums can mean a difference in location of from a few cms to 3.552 km. Recording Localities • The most specific localities are those described by • a) a distance and heading along a path from a nearby and well-defined intersection or fixed persistent point, or • b) two cardinal offset distances from a single persistent nearby feature of small extent.

9. Collecting Data in the Field Recording Coordinates • Decimal degrees are preferred when reading coordinates from a GPS • have higher precision and thus accuracy • But note some recent GPS units record in Decimal seconds to three decimal points • Reduces transcription error (most databases store data in DD) Recording Extent • extent is a measure of the size of the area within which collecting or observations occurred for a given locality – the distance from the point described by the locality and coordinates to the furthest point where collecting or observations occurred in that locality

10. Documentation Example: • Locality: 2 nm NNE of North Head Light House off Sydney Heads • Lat/Long:−33.79916, 151.32054 • Datum:WGS84 • GPS Accuracy:6 m • Extent:50 m • Remarks:Garmin Etrex Summit GPS for coordinates and accuracy

11. Database Fields See: Geospatial Element Definitions v1.4 (extension to Darwin Core) • Decimal Latitude • Decimal Longitude • Geodetic Datum • Maximum Uncertainty Estimate • Maximum Uncertainty Unit • Verbatim Coordinates • Verbatim Coordinate System • Georeference Source (e.g. USGS Gosford Quad map 1:24000, 1973) • Verification Status (e.g.: "requires verification", "verified by collector") • Validation Status • Georeference Determined by • Georeference Determined date • Remarks • [Spatial Fit]

12. Spatial Fit A measure of how well the geometric representation matches the original spatial representation. For an area where the original spatial representation of a locality is the red polygon with area ‘A’. The spatial fit is: 1.0 0 (Pi*r22)/A (Pi*r12)/A (2*r22)/A From J. Wieczorek, in Chapman and Wieczorek (eds) (2006)

13. Geodetic Datums Traditional Horizontal Datums NAD 27 ED 50 (Clarke Ellipsoid ) (International Ellipsoid) From US Navy (n.dat.)

14. Datum Shifts

15. Vertical Datums Like horizontal measurements, elevation only has meaning when referenced to some start point. MSL Elevation HighTide Mean Sea Level Low Tide Mean sea level is the most common vertical datum. From US Navy (n.dat.)

16. MaNiS Georeferencing Calculator http://www.manisnet.org/gc.html

17. Locality Types Features • Named Place (Feature) • Near a Feature • Between Two Features • Street Address Paths • Path • Between Two Paths Offsets • Offset Distance • Offset at a Heading • Offset along a Path • Offset in Orthogonal Directions • Offset from two distinct Paths Coordinates • Longitude and Latitude Coordinates • UTM Coordinates Areas • Township, Range, Section • Map Sheet Do not georeference • Captive or Cultivated • Dubious • Cannot be Located

18. Locality Types • Named Place • Example 1: “Bakersfield” • Example 2: “Point Lookout” • Example 3: “Isla Tiburon” • Example 4: “Junction of Dwight Avenue and Derby Street ” • Georeference: Use centre of named place • Extent: Use the distance from the coordinates of the named place to the furthest point within the named place • Uncertainty: Use the MaNIS Georeference Calculator

19. Example Locality: “Bakersfield”Suppose the coordinates for Bakersfield came from the GNIS database (a gazetteer) and the distance from the center of Bakersfield to the furthest city limit is 3 km. Coordinate System: degrees minutes seconds Latitude: 35º 22' 24" N Longitude: 119 º 1' 4" W Datum: not recorded; 79 m uncertaintyCoordinate Precision: nearest second; 40 m uncertaintyCoordinate Source: gazetteer Extent of Named Place: 3 km Distance Units: km From Georeferencing Calculator Decimal Latitude: 35.37333 Decimal Longitude: -119.01778 Maximum Uncertainty Distance: 3.119 km

20. Locality Types Between two Named Places • Example 1: "between Point Reyes and Inverness" • Georeference:Find the coordinates of the midpoint between the centres of the two named places (e) • Extent:Use the extent of A or B, whichever is greater, plus one-half the distance between the centres of A and B. • Uncertainty: Use the MaNIS Georeference Calculator • Calculate the same as for ‘Named Place’.

21. www.biogeomancer.org BioGeomancer • Introduction - Web Site

22. BioGeomancer Workbench

24. BioGeomancer Workbench – Batch Georeferencing • Need to register and Log in • Submit a project • Use the “Help” to see how to go about submitting files • (See next slide for formatting) • NB – files must be in UTF-8 • Results downloaded as XML file

25. Format for batch georeferencing

26. GeoLocate Similar to BioGeomancer Can use line/polygon features such as distance along a road/river etc. Many features only available (as yet) for USA and Spain. Desktop version, batch mode and collaborative georeferencing http://www.museum.tulane.edu/geolocate/

27. Acknowledgments:

28. http://www.gbif.org/orc/?doc_id=1288 Chapman & Wieczorek (eds) (2006)