LANDSAT satellites are equipped with scanners which record the radiation from the earth surface in four spectral channels. Features on the ground have a "spectral signature": a certain combination of data in the four channels. The records in the four channels represent a four-dimensional feature space, in which each particular feature is characterized by a volume, similar to the CIE color space; the size and location of that volume must be established by identifying that feature on the ground ("ground truth"). The recognition and analysis of features implies the establishment of their spectral signature and a subsequent classification of as many as possible of the picture elements (pixels) into appropriate groups. By means of computer methods, this can be done automatically. The success and the limitations of this procedure will be demonstrated on pictures of snow in the high alpine regions of Switzerland and on land use in the Po valley of Italy.