First, the domain of w3cgeo:lat, w3cgeo:lon and w3cgeo:alt properties is w3cgeo:SpatialThing. While one could interpret these properties as mapping to a geometry, as GeoRSS Simple does, there isn't conclusive evidence that this is what was intended. Second, w3cgeo:Point is defined as a sub-class of w3cgeo:SpatialThing. As a result, we have inconsistency in how w3cgeo:SpatialThing may be interpreted. For example:
First, the domain of w3cgeo:lat, w3cgeo:lon and w3cgeo:alt properties is w3cgeo:SpatialThing. While one could interpret these properties as mapping to a geometry, as GeoRSS Simple does, there isn't conclusive evidence that this is what was intended. Second, w3cgeo:Point is defined as a sub-class of w3cgeo:SpatialThing. As a result, we have inconsistency in how w3cgeo:SpatialThing may be interpreted. For example:
w3cgeo:SpatialThing has lat/lon, some people might equate w3cgeo:SpatialThing with geosparql:Geometry;foaf:Person is defined as a sub-class of w3cgeo:SpatialThing, some other people find it natural to equate w3cgeo:SpatialThing with geosparql:Featurefoaf:Person is defined as a sub-class of w3cgeo:SpatialThing, some other people find it natural to equate w3cgeo:SpatialThing with geosparql:FeatureSo in summary, it's safer to say that our Spatial Thing equates to geosparql:Feature, and that it is not the same as w3cgeo:SpatialThing.
So in summary, it's safer to say that our Spatial Thing equates to geosparql:Feature, and that it is not the same as w3cgeo:SpatialThing.
As can be seen in the example above, the geometry 30505-10 is an attribute of the City of Edinburgh. If your intent is to make a statement about, or refer to, the real-world entity then make sure you link to the Spatial Thing rather than the geometry. Furthermore, note that the geometry record may be updated and re-published with a new identifier, for example, if the city boundary was resurveyed and would then result in a broken link.
As can be seen in the example above, the geometry 30505-10 is an attribute of the City of Edinburgh. If your intent is to make a statement about, or refer to, the real-world entity then make sure you link to the Spatial Thing rather than the geometry. Furthermore, note that the geometry record may be updated and re-published with a new identifier, for example, if the city boundary was resurveyed and would then result in a broken link.
Data publishers should also be aware of a common pattern used in the publication of Linked Data, where the Spatial Thing and the information resource that describes it are identified separately — often, but not always, using /id as part of the URI for Spatial Thing, and /doc for the corresponding page/document/record. When the URI for the Spatial Thing is dereferenced, a HTTP 303 (see other) response is used to redirect the browser to the page/document/record URL. For example:
http://statistics.gov.scot/id/statistical-geography/S12000036 redirects to http://statistics.gov.scot/doc/statistical-geography/S12000036By way of example, let's explore some data for Edinburgh.
-The City of Edinburgh Council Area (e.g. the geographical area that Edinburgh City Council is responsible for) is identified by the Office for National Statistics (the recognized national statistical institute of the UK) using their GSS code (a 9 character alpha numeric identifier) S12000036 and the URI http://statistics.data.gov.uk/id/statistical-geography/S12000036. At the same time, the devolved government in Scotland, operating under its own jurisdiction, retains the GSS code but uses the URI http://statistics.gov.scot/id/statistical-geography/S12000036. Furthermore, the Ordnance Survey maintain yet another URI for the City of Edinburgh Council Area as part of its 'Boundary Line' service that contains administrative and statistical geography areas in the UK: http://data.ordnancesurvey.co.uk/id/7000000000030505. Similarly, Geonames identifies Edinburgh, a second-order administrative division, as http://sws.geonames.org/2650225/. All of these URIs refer to the same Spatial Thing and are equated using owl:sameAs.
The City of Edinburgh Council Area (e.g. the geographical area that Edinburgh City Council is responsible for) is identified by the Office for National Statistics (the recognized national statistical institute of the UK) using their GSS code (a 9 character alpha numeric identifier) S12000036 and the URI http://statistics.data.gov.uk/id/statistical-geography/S12000036. At the same time, the devolved government in Scotland, operating under its own jurisdiction, retains the GSS code but uses the URI http://statistics.gov.scot/id/statistical-geography/S12000036. Furthermore, the Ordnance Survey maintain yet another URI for the City of Edinburgh Council Area as part of its 'Boundary Line' service that contains administrative and statistical geography areas in the UK: http://data.ordnancesurvey.co.uk/id/7000000000030505. Similarly, Geonames identifies Edinburgh, a second-order administrative division, as http://sws.geonames.org/2650225/. All of these URIs refer to the same Spatial Thing and are equated using owl:sameAs.
The example snippet above, provided in [[TURTLE]] format, shows the relationships between the City of Edinburgh district and the electoral wards it contains. Also note that complementary use of geosparql:sfTouches to relate the City of Edinburgh to its adjacent districts; Midlothian, West Lothian etc.
The example snippet above, provided in [[TURTLE]] format, shows the relationships between the City of Edinburgh district and the electoral wards it contains. Also note that complementary use of geosparql:sfTouches to relate the City of Edinburgh to its adjacent districts; Midlothian, West Lothian etc.
A second domain where relationships between Spatial Things and non-spatial resources occur is earth observing. The example below, provided in [[GML]], relates a monitoring point at Deddington on the Nile River, Tasmania, to the sensor that is deployed there (using the sams:hostedProcedure property) and relates that monitoring point to the waterbody whose properties are being measured (using the sam:sampledFeature property). Here, the links are defined using [[XLINK11]].
Unlike administrative areas and other topographic features that have clearly defined boundaries, places often have ill-defined, fuzzy boundaries that are based on human perception of ‘place’; you can’t always define a boundary for a place. For example, Edinburgh the named place, published by Ordnance Survey, is described using only a notional point geometry; information is not provided about the geometric extent. Other examples of places with ill-defined, fuzzy geometries include The Sahara, the American West and Renaissance Italy. The relationships between places, with their ill-defined (or even absent) geometrical extents, defy description using the topological relationships which are computed mathematically from geometry.
+Unlike administrative areas and other topographic features that have clearly defined boundaries, places often have ill-defined, fuzzy boundaries that are based on human perception of ‘place’; you can’t always define a boundary for a place. For example, Edinburgh the named place, published by Ordnance Survey, is described using only a notional point geometry; information is not provided about the geometric extent. Other examples of places with ill-defined, fuzzy geometries include The Sahara, the American West and Renaissance Italy. The relationships between places, with their ill-defined (or even absent) geometrical extents, defy description using the topological relationships which are computed mathematically from geometry.
Given the lack of existing best practice, we propose the use of a qualitative assertion based on human perceptions to relate places that are deemed to be the same: samePlaceAs.