SPARQLMap

Interactive map layout for SPARQL RDF results.

It uses a SPARQL query to load RDF resources with coordinates within the bounds of the map, and renders each as a marker, which shows an info window with HTML representation of the resource when clicked.

Setup

SPARQLMap can be constructed with the following arguments:

map

google.maps.Map

Instance of Google Maps map

endpoint

URL

URL of the SPARQL endpoint

select

string

SPARQL select query string

focusVarName

string

Variable which will be bound to resources that represent markers

graphVarName?

string

Optional graph name variable name, in case marker resources are contained in named graphs

Usage

window.SPARQLMap.geo = new SPARQLMap.Geo(window.SPARQLMap.map, new URL('http://dbpedia.org/sparql'), `SELECT ?s { ?s ?p ?o }`, 's', 'g'); // construct object
window.LinkedDataHub.map.addListener('idle', function() { window.SPARQLMap.geo.loadMarkers(window.SPARQLMap.geo.addMarkers); }); // binds a handler for the 'idle' event

The library can be built using the webpack command; a browser-ready distribution will be created in the dist folder.

Query building

SPARQLMap will take the initial SELECT query, append a pattern that selects and filters the coordinates using the current viewport bounds (from the specified default and optionally named graph), and wraps it into a DESCRIBE.

Example

Initial SELECT:

SELECT ?s
{
    ?s ?p ?o
}

Default graph

Given focusVarName = 's' and current viewport bounds ((51.067080526460764, -2.8555919369506944), (51.905101013931514, 0.07458193695067283)), the final query executed on the endpoint will look like this:

PREFIX  geo:  <http://www.w3.org/2003/01/geo/wgs84_pos#>
PREFIX  xsd:  <http://www.w3.org/2001/XMLSchema#>

DESCRIBE ?s
WHERE
  { SELECT  ?s
    WHERE
      { ?s  ?p  ?o
        { ?s  geo:lat   ?lat ;
              geo:long  ?long
          FILTER ( ?long < 56.882781982421875 )
          FILTER ( ?lat < 66.28570153405012 )
          FILTER ( ?lat > 42.00247670093502 )
          FILTER ( ?long > -36.88278198242187 )
        }
      }
  }

Named graph

Given focusVarName = 's', graphVarName = 'g' and current viewport bounds ((51.067080526460764, -2.8555919369506944), (51.905101013931514, 0.07458193695067283)), the final query executed on the endpoint will look like this:

PREFIX  geo:  <http://www.w3.org/2003/01/geo/wgs84_pos#>
PREFIX  xsd:  <http://www.w3.org/2001/XMLSchema#>

DESCRIBE ?s
WHERE
  { SELECT  ?s
    WHERE
      { ?s  ?p  ?o
          { ?s  geo:lat   ?lat ;
                geo:long  ?long
            FILTER ( ?long < 56.882781982421875 )
            FILTER ( ?lat < 66.28570153405012 )
            FILTER ( ?lat > 42.00247670093502 )
            FILTER ( ?long > -36.88278198242187 )
          }
        UNION
          { GRAPH ?g
              { { ?s  geo:lat   ?lat ;
                      geo:long  ?long
                  FILTER ( ?long < 56.882781982421875 )
                  FILTER ( ?lat < 66.28570153405012 )
                  FILTER ( ?lat > 42.00247670093502 )
                  FILTER ( ?long > -36.88278198242187 )
                }
              }
          }
      }
  }

RDF data conventions

SPARQLMap will currently

• only recognize geo:lat and geo:long (from the WGS84 Geo vocabulary) properties as coordinates.
• use foaf:isPrimaryTopicOf and, as a fallback, foaf:page values as URLs to load info window HTML from when a marker is clicked. Absent these properties, the info window will not be available for that resource.