1. Method of calculating and encoding a score of semantic and spatial similarity between concepts of an ontology stored in hierarchically numbered trellis form, each concept of the trellis having an associated identifier comprising at least one path, each path consisting of a series of integers and corresponding to a succession of arcs oriented between the concept to which said at least one path is allocated and the universal concept to form a hierarchy of concepts under the universal concept, each path associated with said concept defining a route through successive parent, respectively child, concepts, making it possible to reach the concept, wherein the method consists at least in calculating and encoding a semantic and spatial similarity score by convergence relative to their common semantic characteristics respectively by separation according to their spatial distance for each concept with respect to a central concept, taken two-by-two.