Presentation on theme: "Elements to georeference data without coordinates."— Presentation transcript:
Elements to georeference data without coordinates
Case study Some data may not have coordinates attached but only a locality name or a direction Lets say: Accipiter, Matadi, Bas-Congo, DRC, 1963
New concepts Well try to assign estimated coordinates accompanied by an estimation of the error margin (error radius) Well base ourselves (there) on the methodology georeferencung for dummies elaboratred by the University of Berkeley for the MaNIS, HerpNET and Ornis project (also recommended by GBIF and Arthur Chapman http://www.herpnet.org/herpnet/documents/geo reffordummy.xls http://www.herpnet.org/herpnet/documents/geo reffordummy.xls
New concepts Uses the Georeferencing Calculator (Applet) to calculate the final error radius (combination from the gazetteer data and metadata of the Datum) http://manisnet.org/gci2.html
Gazetteer and Voronoï Most of time a gazetteer (list of localities and coordinates) is made up of poitn data …while a locality in an area (polygon) Voronoï is a possible methodology to attach extent to points
Gazetteer and Voronoï Exercise: -Import the Congolese Gazetteer (available via DIVA GIS) into QGIS -Convert it into a shapefile -Add labels with the name of localities and localize Matadi (West of DRC, about 100km to the Atlantic Ocean)
Create Voronoï areas Exercise: -Import the Congolese Gazetteer (available via DIVA GIS) into QGIS -Convert it into a shapefile -Add labels with the name of localities and localize Matadi (West of DRC, about 100km to the Atlantic Ocean) Lat: -5.8166 Long 13.45
Voronoï On GIS – Vector tab – Geometry tools – Voronoï poygons – Select the Shapefile to proceed – Declare the shapefile containing the output:
Voronoï Output shapefile attaches areas to the localites (perpendicular to the halfways of neighbouring points)
Voronoï Determinining the furthest point within the area is easy Enable UTM conversion to have meter value
Voronoï Is there any drawbacks with that method?
Voronoï Is there any drawbacks with that method? – Do not work when a place is part of another place – The date of the gazetteer must correspond to the date of the actual original data (urbanization ois a dynamical process)
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