The exploration of the features presented by the training sets of each class (size, shape and orientation) in order to construct the respective decision regions borders without making explicitly any statistical hypothesis is presented in this paper. Its incorporation allows defining more correct decision borders since there is a significant improvement in the classification rates obtained. Mathematical morphology operators are preferentially used in this methodology, which is illustrated with two spectral features (wetness' tasselled cap and NDVl's vegetation index) of seven land cover classes constructed from Landsat TM satellite images of central Portugal.