Advances in image processing systems during the last decade have made practical the development of an information system for archaeology that combines large scale maps, a conventional database management system, and image data coming either from air photography or geophysical prospecting. The maps must be coded and compressed for permanent, as well as on-line, storage. Two coding schemes were tried, one for permanent long-term storage on magnetic tape, the other for on-line storage during processing. For quick acess we use a single bit of information per original picture element. The bit code gives compression of eight over the grayscale original. Statistical analysis of typical maps has shown that in the neighborhood of built-up areas, compression of three times or more can be obtained by the use of simple runlength code. More complex coding schemes, which use code lengths in rough inverse proportion to the probibility of runlength occurrence, give higher compression still while retaining block length properties suitable for recording on magnetic tape.