The explanatory note gives definitions and explains degrees of desertification hazard. Criteria are given for the different bioclimates, distinguished on the accompanying maps. Four classes of vulnerability to desertification are considered: areas of sand movement, areas subject to stripping by deflation and/or sheetwash, areas subject to accelerated gully erosion, and areas subject to progressive salinization/alkalinization. Population and animal densities have been used as a measure of human and animal pressure on the land