Abstract: A method of localising portable apparatus (200) obtains: a stored experience data set comprising a set of connected nodes; captured location representation data provided by at least one sensor associated with the portable apparatus, and a current pose estimate of the portable apparatus within the environment. The pose estimate is used to select a candidate set of the nodes that contain a potential match for the captured location representation data. The pose estimate is used to obtain a set of paths from path memory data, each said path comprising a set of said nodes previously traversed in the environment under similar environmental/visual conditions. The set of paths is used to refine the candidate set. The captured location representation data and the refined candidate set of nodes is compared in order to identify a current pose of the portable apparatus within the environment.