PREFIX ewi: <http://ewi.mmlab.be/ns#>
PREFIX prov: <http://www.w3.org/ns/prov#>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
SELECT DISTINCT ?location ?label WHERE {
    ?s ewi:location ?location .
OPTIONAL { ?location rdfs:label ?label }
}