SDTS GIS format. Geographic information standard used by the U.S. Geological Survey. Used for archiving and exchanging maps and map data. SDTS is an acronym for Spatial Data Transfer Standard. Based on ISO 8211. U.S. Federal Information Processing Standard. An SDTS transfer archive consists of multiple .ddf files, typically combined in a .tar.gz file. The file extension .ddf is derived from Data Descriptive File. Binary format. Contains digital line graphs (DLG). Digital line graphs are vector data commonly used for maps. Digital elevation models are stored as a raster of elevation values.