Method of distinguishing various types of vegetation, rocks, etc. formerly using either monochrome or coloured infrared film which can be used in conventional cameras, but nowadays using an infrared sensor. Potentially, aerial photography using an infrared camera may be of benefit in preparing geologic maps. Longer-wavelength infrared can discriminate most rocks, shorter wavelengths can reveal iron oxide, etc.; alteration effects around certain mineral deposits, e.g. porphyry coppers with their attendant clay minerals, can also be distinguished, and the technique allows a consideration of plant species affected by the nature of the soil and rock substrate.