The role of remote sensing is well known and can be successfully applied as an initial step in surface geologic exploration. The aim of this study, by means of Landsat TM 7 image interpretation, is to assist photogeologic map compiling, which will serve as a core document for an upcoming field mapping exercise. The mathematical background and the wide variety of math-method possibilities offered by a satellite image interpretation software were used for this purpose. In this way the requested preliminary photogeologic map was compiled, based on the spectral properties of the surface geologic formations. Fortunately the areas of interest were in a desert area (Central Libya), so there was no limitation by vegetation coverage to hinder the application of spectral properties to geologic formations. After the geocoding of the images the display of different compositions of the Landsat TM 7 registration channels was begun. Contrast enhancement and histogram fitting were applied, and further operations to highlight some hidden properties of the original dataset were performed. Thus, some filters from the set offered by the software, some edge enhancement and finally the two types of classification (unsupervised and supervised), were applied.