Hi Andreas,
thanks for the input. I have drafted the current text about geo-related datatypes, but I am far from being an expert in this area. Our mapping expert in Wikidata is Katie (Aude), who has also been working with OpenStreetMap, but further expert input on this topic would be quite valuable.
As in all areas, we need to find a balance between generality and usability, so I am slightly in favour of committing to one SR for now (as I understand, the data can be converted easily between SRs but -- as opposed to other cases where people measure something -- most of the world seems to be happy with one of them).
I have now included a link to this thread into an editorial remark in the data model, so we do not forget about this discussion when working out the details.
Markus
On 04/04/12 14:16, Andreas Trawoeger wrote:
Hi everybody!
As the guy who has to honor to shortly receive some funding from Wikimedia Germany for handling spatial open government data [0] I would like to make some remarks on the current geo definitions in the Wikidata model:
- Spatial Reference System Identifier (SRID [1]) definition is missing
Every GeoCoordinatesValue field should either have a corresponding SRID field that defines the used spatial reference system (SRS [2]) or mandate the use of a single SRS like WGS84 [3] which is currently the standard used by GPS, OpenStreetMap and Wikipedia.
- Geographic shapes should be defined in either Well-known text (WKT
[4]) or GeoJSON [5]
WKT is the defacto standard to store spatial data in a rational database and GeoJSON is the defacto standard to access geo data via web. Both formats can be easily transformed into each other. So which one you choose pretty much depends on your preferred choice of SQL vs. NoSQL database.
So in summary I would propose the following data model for spatial data:
Geographic locations Datatype IRI: http://wikidata.org/vocabulary/datatype_geocoords Value: GeoCoordinatesValue Mandatory spatial reference system: EPSG 4326 (WGS 84/GPS) Type: Decimal
Geographic objects Datatype IRI: http://wikidata.org/vocabulary/datatype_geoobjects Value: GeoObjectsValue Type: GeoJSON [5]
Geographic objects SRID Datatype IRI: http://wikidata.org/vocabulary/datatype_geoobjects_srid Value: GeoObjectsSridValue Type: EPSG Spatial Reference System Identifier (SRID [1])
That model would allow a structure where every spatial object can have a complex geometry stored in its original geodetic system and still have an easily manageable location in GPS format.
cu andreas
[0] http://de.wikipedia.org/wiki/Wikipedia:Community-Projektbudget#2._kartenwerk... [1] https://en.wikipedia.org/wiki/Spatial_reference_system_identifier [2] https://en.wikipedia.org/wiki/Spatial_reference_system [3] https://en.wikipedia.org/wiki/WGS84 [4] https://en.wikipedia.org/wiki/Well-known_text [5] https://en.wikipedia.org/wiki/GeoJSON
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