For a specifical climatic zone, the soil types and units generally used in many different purposes soil mapping are closely related to geomorphological and rock parent characteristics. These relations are much more pronounced in mountainous areas. This paper proposes an objective and easily repeatable method to perform soil mapping on the basis of units likely used on geological and geomorphological mapping, complemented with numerical slope data derived of the Digital Terrain Model. The analysis and combination of this information has been done within a Geographical Information System, which is a ideal tool to develop this application