1. Georeferencing Workshop Rebecca J. Rowe University of Chicago Committee on Evolutionary Biology & Division of Mammals The Field Museum

2. Outline What is georeferencing? Introduce the point-radius methodology Introduce georeferencing tools Work through some examples

3. Georeferencing is the expression of a spatial description in coordinates within a frame of reference

4. Coordinates alone are not enough Latitude and longitude (in a consistent format) Uncertainty (maximum error distance) Frame of Reference (i.e. datum)

5. Retrospective Georeferencing From textual descriptors: determine coordinates assign spatial uncertainty From collector determined coordinates: convert coordinates (if necessary) assign spatial uncertainty

6. Textual Descriptors Bakersfield Near Bakersfield 10 mi E (by air) Bakersfield 5 mi from Bakersfield 2 mi E and 1.5 mi N of Bakersfield 13 mi E (by road) Bakersfield 10.2 mi E of Bakersfield

7. Coordinate Systems decimal degrees 35.3733, -119.0178 degrees minutes seconds 35° 22 23.88 N, 119 1 4.08 W degrees, decimal minutes 35 ° 22.398 N, 119 1.068 W UTM Zone 11S 316695E 3916111N

8. The Ultimate Goal Spatially explicit link between the identity of a voucher, and the collection event Increases data for biological distribution & diversity studies Enables computer based geographic analyses

9. The Ultimate Goal Spatially explicit link between the identity of a voucher, and the collection event Increases body of data for biological distribution and diversity studies Enables computer-based geographic analyses

10. The Ultimate Goal Spatial Uncertainty The geographic area encompassing all possible locations for the point

11. Georeferencing, the how to

12. Choosing the right georeferencing method is a compromise between precision, accuracy, and speed

13. The Point-Radius Method Uses one set of coordinates, the datum, and a bounding radius to describe a locality Can incorporate both manual and automated georeferencing methods Is a reproducible process

14. Davis, Yolo County, California

16. Accuracy & Precision Accurate but not precise: Illinois, Chicago Precise but not accurate: Kelley Canyon, Z11 625200E, 4368390N –Correct UTM zone is 12

17. Accuracy & Precision The georeferencing process aims to increase both the accuracy of the locality descriptor and the locality precision

18. Spatial Uncertainty a.k.a maximum error distance Captures the original inaccuracy and/or imprecision documented by the collector Additional error introduced during data entry or the georeferencing process

19. What contributes to uncertainty? Locality extent GPS accuracy Unknown datum Imprecision in distance Imprecision in direction Imprecision in coordinates Map scale Combinations of the above

20. Out of context, you can’t assume what the collector meant!

21. Locality Extent Named places are not single points Use the geographic center of a place & measure the greatest extent for the uncertainty In general, current extents will be greater than historical ones, yielding conservative measures

22. Davis, Yolo County, California

23. GPS Accuracy Deliberate signal scrambling before May 2000, artificial inaccuracies of ~ 100 m Accuracy recorded on the GPS unit can be misleading Best to assume 30m accuracy for retrospective GPS coordinates after May 2000

24. Unknown Datum Geodetic datums define the size and shape of the earth and the origin and orientation of the coordinate systems used to map the earth Without a datum, coordinates are like measures without units.

25. Datums Frames of Reference: Australian Geodetic 1984 Japanese Geodetic Datum 2000 North American Datum (NAD) 1927 North American Datum (NAD) 1983 South American 1969 World Geodetic System (WGS) 1984

26. Datums, how do they vary?

27. Why is the datum important?

28. Extent of Offset

29. Distance 10.5 mi N of Bakersfield - the fraction is ½, uncertainty = 0.5 mi 10.6 mi N of Bakersfield - fraction is 6/10, uncertainty = 0.1 mi 10.75 mi N of Bakersfield - fraction is ¾, uncertainty = 0.25 mi In general, use 0.5 times powers of ten

30. Direction 10 mi N of Bakersfield - uncertainty 45 degrees in either direction 10 mi NE of Bakersfield - uncertainty is 22.5 degrees, ENE - NNE 10 mi N and 5 mi E of Bakersfield - can ignore directional imprecision

31. Coordinate Precision Too few digits = unnecessary uncertainties 1° does not equal the same distance everywhere on the surface of the earth

32. Map Scale Each map has an inherent level of accuracy USGS Map Accuracy (1/30 to 1/50 inch) For non-USGS use NOAA standard of 1 mm

33. Georeferencing Calculator Example: 1.3 km N, 0.6 km E Confluence Brumley & Pack Creeks, La Sal Mtns, Utah. http://elib.cs.berkeley.edu/manis/gc.html

34. Sources of Coordinates Maps Gazetteers Localities already recorded with coordinates http://www.indexmundi.com/zp/ http://geonames.usgs.gov/

35. N side Clear Creek Campground, Raft River Mtns, Utah T13N R13W Sec 10 Options: TRS Converter & pre-established uncertainty http://www.esg.montana.edu/gl/trs-data.html Use a map and measure section geocenter Georeference to the campground Demonstrate TOPO program Example

36. Elevation Collector recorded elevation values are not incorporated in the georeferencing process There is often no record of source & precision Can be helpful guide in identifying errors

37. Before you start, plan Georeferencing is time-consuming Georeferencing errors will occur Certain descriptors won’t be georeferenced A common framework for data collection is essential

38. Increasing Efficiency What not to do: Do not georeference specimen by specimen! Do not treat the collections individually!

39. Increasing Efficiency What to do: Compile unique localities across all collections Divide that list geographically and redistribute Use your expertise Assign georeferencing tasks by small spatial units (e.g. counties or provinces) Within those units sort localities by place name Coordinate the purchasing of georeferencing aids

40. Example

41. MaNIS Framework

42. Error detection Map the coordinates (ArcView): Do the coordinates have the correct + or – sign? Is the decimal place shifted over (e.g. -111.90000 vs. -1119.0000) Does the latitude = longitude or vice versa? Do they fall within the correct geographical unit?

43. Error Checking Egypt

44. Error Checking Egypt http://www.cia.gov/cia/publications/factbook/

45. Extra slides if TOPO fails