An effort was made to produce the best Thematic Mapper colour image for detailed geological visual interpretation. Northern Somalia sedimentary rocks, ranging in age from Jurassic to Quaternary, were chosen as test-object, Bands 7 and 1 were selected as giving the best colour composite; decorrelation stretching with spatial filtering of principal components was chosen as the most suitable enhancement technique. Improved image characteristics facilitate recognition and mapping of lithologic units which can be used to frame ongoing stratigraphical studies for the area under investigation.