1. An information handling method in which information items are mapped to respective nodes in an array of nodes by mutual similarity of said information items, such that similar information items map to nodes at similar positions in said array of nodes; a mapping relationship being defined between feature data relating to an information item and nodes in said array of nodes; said method comprising the steps of: (a) for each of a group of information items: detecting feature data representing each of a set of properties of that information item; (b) for the ensemble of feature data corresponding to said group of information items: detecting more significant and less significant properties within said ensemble; associating said feature data relating to more significant properties so as to generate a reduced feature vector for each information item; (c) defining a mapping between said reduced feature vectors and nodes in said array of nodes.