Embodiments of the present invention relate to a route-planning device (200;302) comprising a storage section (230;306) storing map information, the map information including information identifying a plurality of potential positions, each potential position corresponding to a position at which a location of a predetermined type might potentially be found; and a search route module (490) arranged to determine a search route visiting at least one of the potential positions, the determination of the search route using a predetermined efficiency measure based on likelihood of finding a location of the predetermined type.