1. An information handling method performed by an information processing device to map information items 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 elements relating to an information item and nodes in said array of nodes; each feature data element belonging to one of a plurality of feature classes; said method comprising the steps of: for each of a group of information items: detecting, at a processor, from an information item, feature data elements representing each of a set of properties of that information item; for the ensemble of feature data elements corresponding to said group of information items: detecting, at the processor, more significant and less significant properties in respect to each feature class within said ensemble, at least one property being detected as a less significant property; associating, at the processor, said feature data elements relating to more significant properties in respect to each feature class; concatenating, at the processor, only said associated feature data elements relating to more significant properties so as to generate a reduced feature vector for each information item, the reduced feature vector including only more significant properties; and defining, at the processor, a mapping between said reduced feature vectors and nodes in said array of nodes.