The soil type and conservation practices were mapped based on
the 1:50000 geological map and the aerial panchromatic coverage
acquired in 2002 at the 1:20000 scale by the Direction Regionale
des Eaux et For^ets (DREF) of Marrakech. As soil protection was not
directly visible on remotely sensed documents, it was estimated
using recorded field measurements based on landscape stratification,
intersecting the geological map with the land use types
interpreted from the aerial photographs. Soil surface characteristics
were observed on these landscape units along transects (one
observation every 20 cm along 20 m lines). The main variables
observed were the stone, vegetation and bare soil coverage,
allowing computation of the fraction of soil protected by stones or
vegetation.