A method and a system for evaluating the class of a test datum in an original metric space, each datum belonging to at least one class grouping a plurality of data, includes a step of graphical representation of the spatial organization of a set of learning data of the original space in a representation metric space, a conjoint membership level indicating if any two data from the learning set belong to the same class. The method also includes a step of relating the test datum to the projections of the data from the learning set, the most probable class of the test datum being the class of the projections of the data from the learning set related to the test datum. Application: assistance with decision-making in discrimination, shape recognition.