Georeferences
Definition: http://rs.tdwg.org/dwc/terms/index.htm#coordinatePrecision
Translations: http://terms.tdwg.org/wiki/dwc:coordinatePrecision
Question: Does anyone record or serve coordinatePrecision? If so, can you explain how researchers might find this information useful?
Answer: The term coordinatePrecision is populated fairly often, especially in contexts that use grid cells based on geographic coordinates (e.g., 1 degree grid cell). In this context, in the absence of coordinateUncertaintyInMeters or footprintWKT, a point-radius or bounding box could be determined from the decimalLatitude, decimalLongitude and coordinatePrecision. The term coordinatePrecision could be used in records that have coordinateUncertaintyInMeters as well to highlight that the coordinates, as given, are of a particular precision that cannot be captured by the coordinates themselves (e.g., the coordinates 34.5, -117.25 could refer to a location with indeterminate very high precision, or roughly, to a location with a precision of a 15 minutes). If the coordinateUncertaintyInMeters is given and calculated faithfully, the coordinatePrecision adds an indicator of how much of the uncertainty is due to imprecision.
Researchers would find coordinatePrecision particularly useful to understand how specific the coordinates are in the absence of a point-radius or other geometry.
Question: What are acceptable values for coordinatePrecision?
Answer: Following is a table showing the English language equivalent and the coordinatePrecision value. The coordinatePrecision value of any missing precisions should be possible to interpolate.
| coordinate precision | coordinatePrecision |
|---|---|
| nearest degree | 1 |
| nearest half degree | 0.5 |
| nearest quarter of a degree | 0.25 |
| nearest tenth of a degree | 0.1 |
| nearest hundredth of a degree | 0.01 |
| nearest thousandth of a degree | 0.001 |
| degree to four decimal places | 0.0001 |
| *degree to five decimal places | 0.00001 |
| nearest 10 minutes | 0.1666667 |
| nearest minute | 0.0166667 |
| nearest tenth of a minute | 0.0016667 |
| nearest hundredth of a minute | 0.0001667 |
| *nearest thousandth of a minute | 0.0000167 |
| nearest 10 seconds | 0.0027778 |
| nearest second | 0.0002778 |
| nearest tenth of a second | 0.0000278 |
| *nearest hundredth of a second | 0.0000028 |
* these three levels of precision are commonly found on commercial GPS devices in the three modes: decimal degrees, degrees decimal minutes, and degrees minutes seconds.
There is a nice treatment of accuracy and precision, including references to GPS capabilities, at http://gis.stackexchange.com/questions/8650/measuring-accuracy-of-latitude-and-longitude.
Definition: http://rs.tdwg.org/dwc/terms/index.htm#georeferenceVerificationStatus
Translations: http://terms.tdwg.org/wiki/dwc:georeferenceVerificationStatus
Lookup table: https://github.com/tucotuco/DwCVocabs/blob/master/vocabs/georeferenceVerificationstatus.txt
Question: Do you use the georeferenceVerificationStatus field? Do you know if or how researchers have used this field?
Answer: The intention of the georeferenceVerificationStatus field is to avoid repeating work unnecessarily. Darwin Core documentation of georeferenceVerificationStatus recommends exactly three possible non-null values for this field ('verified by collector', 'verified by curator', and 'requires verification'). The utility of this field is best realized in the source data to distinguish between georeferences that are as good as they could ever be ('verified by collector'), from those that have had lesser degrees of validation. To be 'verified by collector' means that the collector has seen the occurrence mapped and verified that no more specific georeference can be made. In the absence of the collector's verification, 'verified by curator' indicates that all available resources (which ought to be captured in georeferenceSources) have been use to make the georeference as specific as it can be. Both of these verification statuses indicate to a researcher (and indeed to the data custodian) that there is little that can be done to improve on the georeference, thus avoiding unnecessary work in those cases where questions about the veracity of the georeference arise. Any other state of a record should have a georeferenceVerificationStatus of 'requires verification'.
In all cases, the field georeferencedBy should indicate the person responsible for asserting the veracity of the georeference as given. The georeferenceVerificationStatus field is in common use in collections that value georeferences and the effort expended to determine them, because georeferencing well is not trivial.
For a list of distinct values of georeferenceVerificationStatus and how often they appear in VertNet as of 2017-02-11, see https://gist.github.com/tucotuco/b090a4728010d05601edfccfb982e5ea.
For a list of distinct values of georeferenceVerificationStatus and the recommended standard values for them, see https://github.com/tucotuco/DwCVocabs/blob/master/kurator/georeferenceverificationstatus.txt.
Prior to publishing data sets to IPT, participating partners in VertNet use a lookup file to translate original values of this field (or provide the value 'requires verification' if no such field exists in the original data) to standard values.
Definition: http://rs.tdwg.org/dwc/terms/index.htm#pointRadiusSpatialFit
Translations: http://terms.tdwg.org/wiki/dwc:pointRadiusSpatialFit
Further explanation: Guide to Best Practices for Georeferencing Chapter "Georeferencing Legacy Data" Section 6, "Determining Spatial Fit".
Question: Does anyone record or serve pointRadiusSpatialFit? If so, can you explain how researchers might find this information useful?
Answer: This field is rarely used. It is meant to give a measure of how well the point-radius matches the actual geometry of the locality. A researcher could use it as a filter to distinguish between localities that are well-represented by the point-radius (pointRadiusSpatialFit very close to 1.0) from those that are not (pointRadiusSpatialFit = 0, null, or much greater than 1). Unless the pointRadiusSpatialFit is 1, 0, or null, or the original geometry is a bounding box, the pointRadiusSpatialFit can be onerous to determine.