What is an Aperture Card? Aperture cards have developed from the old IBM80 column punch cards. They are basically a piece of card that is normally 82.5mm x 187mm in size with an area of the card dedicated to one frame of 35mm microfilm. Traditionally aperture cards have been used to store the microfilm copy of large engineering drawings and maps.
Microfilm: A film bearing a photographic record on a reduced scale of printed or other graphic matter. The long answer... Microfilming, also called microphotography, consists in the reduction of images to such a small size that they cannot be read without optical assistance.