Author: Lee Belbin, August 2019
Darwin Core is the most used international standard for describing species occurrence records (observation of species and specimen records): see http://rs.tdwg.org/dwc/terms/). The ALA uses this standard in its main database of records. The Darwin Core terms can be used for finding and filtering occurrence records. These terms are a subset of the available facets in the ALA: terms that are indexed in the main ALA records database.
Once a species has been mapped in the Spatial Portal (Add to Map | Species), the records can be filtered by location information. Alternatively, you can find a suite of species records that have a combination of characteristics such as the records have come from a single institution and belong to the same genus. This is done in the Spatial Portal by Add to Map | Facet.
The following Darwin Core terms (with syntax as per the standard) include some form of location information:
- higherGeography, e.g., Antártida e Islas del Atlántico Sur, Territorio Nacional de la Tierra del Fuego, Argentina
- continent, e.g., Africa
- waterBody, e.g., Tasman Sea
- islandGroup, e.g., Coral Sea Islands
- island, e.g., Maria Island
- country, e.g., Australia
- stateProvince, e.g., Tasmania
- municipality, e.g., Sorell
- locality, e.g., 5km NW of Dunalley
- decimalLatitude, e.g., -41.625
- decimalLogitude, e.g., 148.091
- footprintWKT, e.g., MULTIPOLYGON (((140.020751953125 -32.11514862261243, 140.811767578125 -32.11514862261243, 140.811767578125 -31.83089906339438, 140.020751953125 -31.83089906339438, 140.020751953125 -32.11514862261243)))
Given that there are over 200 Darwin Core terms, it is highly unlikely that all location terms will have been entered into the record by an observer/collector. The majority of records will hopefully have dwc:decimalLatitude and dwc:decimalLongitude and, therefore, terms like dwc:country and dwc:stateProvince can be inferred from latitude and longitude.
What if those values are not accurate or precise? Where there is doubt and where additional location terms are populated, the user may be able to validate the supplied longitude and latitude.
Currently, while all Darwin Core terms are indexed in the ALA, not all are exposed as facets. This is being addressed. We can however demonstrate with those facets that are exposed. Let us take an example where we want to look at the distribution of the tree Eucalytpus gunnii (Cider gum) which is to be found mainly in Tasmania but does occur elsewhere. In the Spatial Portal, do the following
- Add to Map | Species | Eucalyptus gunnii (about 1811 records)
- Select the species from the list presented
- Leave the other fields to default values
- Examine the distribution of the species (Tasmania, ACT, NSW, Queensland, New Zealand and UK).
Say that we are purists and want to examine the distribution in the species main State of Tasmania? We can do that by filtering. Do the following
- Go to the layer legend in the Spatial Portal (called Edit layer options) and click on the drop down box next to Facet
- This is a list of the available facets (which are around 700 strong!) and under the Location section, select State/Territory. This is in fact equivalent to the Darwin Core term stateProvince.
- You will see the list of classes in the records for State/Territory and those classes are sorted by decreasing number of associated records. Tasmania should have about 1671 records.
- Clicking on the box to the left of Tasmania will then select and display on the map, only those records.
- You can if you wish, then create a new species layer by clicking on Create layer with selection. If you do, the new layer will contain only those records that occur in Tasmania (Figure 1).
Figure 1. Eucalyptus gunnii in Tasmania
As an alternative, you can always export any of the records using the full Darwin Core format download option. This is done in the Spatial Portal by using Menu | Export | Points.
After pressing the Next button, you will see the downloads option screen (Figure 2)-
…where you can select Full Darwin Core. The downloaded zip file will contain the following files:
- Citation.csv (sources of the exported records)
- Headings.csv (gory details of each of the column headings/columns – all 140 in this case!)
- README.html (details of the download including a DOI)
- Recordsdate.csv or similar (the occurrence records)
Most of the Darwin Core Location Class terms refer to an area. Without values for latitude and longitude, the observation of a species can only be defined to the resolution of some form of area. For example, if a Local Government Area such as “Sorell” was the only location information (dwc:StateProvince), we can only say that the species occurred somewhere in that area.
While dwc:locality could in theory refer to a point, e.g., “5km NW of Dunalley”, the reality of such a location is better considered as something like “4-6km west to north of Dunalley”: an area.