Circum-Arctic Map of <a href="https://en.wikipedia.org/wiki/Permafrost" class="extiw" title="en:Permafrost">Permafrost</a> and Ground Ice Conditions
Brown, J., O.J. Ferrians, Jr., J.A. Heginbottom, and E.S. Melnikov. 1998, revised February 2001. Circum-arctic map of permafrost and ground ice conditions. Boulder, CO: National Snow and Ice Data Center/World Data Center for Glaciology
<a rel="nofollow" class="external free" href="http://nsidc.org/data/docs/fgdc/ggd318_map_circumarctic/index.html">http://nsidc.org/data/docs/fgdc/ggd318_map_circumarctic/index.html</a>