The Circum-Arctic permafrost and ground ice map is available via ftp in ESRI Shapefile format and Equal-Area Scalable Earth Grid (EASE-Grid) format. See the Format section for an explanation of the files provided via FTP. The circumpolar permafrost and ground ice data contribute to a unified international data set that depicts the distribution and properties of permafrost and ground ice in the Northern Hemisphere (20°N to 90°N). The re-gridded data set shows discontinuous, sporadic, or isolated permafrost boundaries. Permafrost extent is estimated in percent area (90-100 percent, 50-90 percent, 10-50 percent, <10 percent, and no permafrost). Relative abundance of ground ice in the upper 20 m is estimated in percent volume (>20 percent, 10-20 percent, <10 percent, and 0 percent). The data set also contains the location of subsea and relict permafrost. the gridded data are gridded at 12.5 km, 25 km, and 0.5 degree resolution. The shapefiles were derived from the original 1:10,000,000 paper map (Brown et al. 1997) Permafrost, or permanently frozen ground, is ground (soil, sediment, or rock) that remains at or below 0°C for at least two years (Permafrost Subcommittee, 1988). It occurs both on land and beneath offshore arctic continental shelves, and underlies about 22 percent of the Earth's land surface. For more information on the creation of the original map, see Heginbottom et al. (1993). The original paper map also includes information on the relative abundance of ice wedges, massive ice bodies and Pingos, ranges of permafrost temperature and thickness (Brown et al. 1997).