From AMS Glossary
(Popularly called fax chart, fax map.) In meteorology, any display form of weather information, usually a type of synoptic chart, that has been reproduced by facsimile equipment.
Master charts are plotted and analyzed at central weather stations and are transmitted to individual weather stations. Other fields of data are developed by local software from an array of digital data supplied by regional centers. Transmission of weather information by facsimile is rapidly becoming obsolete.