In an earlier article we wrote about the merits of Linked Data and the potential of using RDF as a universal data model for geographical data. We promised some real Linked Data to become available. Well, that time has come. We have placed our national registration of Addresses and Building (BAG) online as Linked Data. You can find it at http://lod.geodan.nl/BAG/. Feel free to play around with it. Maybe you will notice some interesting things, like:

1. The resource classes have Dutch names (they are the official terms used in the BAG), but English explanations are provided.
2. Geometries are coded as Well Known Text (WKT). This complies with an OGC draft standard for RDF and SPARQL: GeoSPARQL. At this moment there is a running request for comments on this possible new OGC standard. The request end on August 5.
3. Geometries are published in two coordinate reference systems: the Dutch National Grid (Rijksdriehoekstelsel) and longitude-latitude with the WGS84 datum.
4. For settlements, we have provided links to extended data in the DBPedia dataset. This is to demonstrate we are acting in the spirit of Linked Data, which advocates to link data wherever this is possible and meaningful.
5. The data are stored in a RDBMS. We made use of D2R Server to make data available as Linked Data (RDF).
6. D2R server also gives us a SPARQL end point, so the dataset (which consists of millions of triples) can be queried. An example of a SPARQL query is:

SELECT ?huisnummer ?openbare_ruimte ?woonplaats
WHERE {
 ?huisnummer <http://lod.geodan.nl/BAG/vocab/resource/nummeraanduiding_huisnummer>  "1"^^xsd:string .
 ?huisnummer <http://lod.geodan.nl/BAG/vocab/resource/openbareruimte>  ?openbare_ruimte .
 ?openbare_ruimte <http://lod.geodan.nl/BAG/vocab/resource/openbareruimte_naam>  "President Kennedylaan"^^xsd:string .
 ?openbare_ruimte <http://lod.geodan.nl/BAG/vocab/resource/woonplaats> ?woonplaats .
 ?woonplaats <http://lod.geodan.nl/BAG/vocab/resource/woonplaats_naam> "Amsterdam"^^xsd:string
}

This returns data on the address “President Kennedylaan 1, Amsterdam”, which is where one of the Geodan offices is located.

So what is next? Now that we have got some real Linked geographical Data online, it seems time to focus using those data in a meaningful way. One thing that people like to do with geographical data is put them in a map. With geometries being available in the WKT format, it shouldn’t be very difficult to create a web mapping app that can tap into the Linked Data cloud. Or is it?