Soil erosion is a prominent cause of land degradation and desertification in Mediterranean countries. The detrimental effects of soil erosion are exemplified in climate (in particular climate change), topography, human activities and natural disasters. Modelling of erosion and deposition in complex terrains within a geographic information system (GIS) requires reliable estimation of topographic factors, as well as the formulation of erosion models adequate for digital representation of spatially distributed parameters. In the current paper, two different approaches for the estimation of erosion in the Sperchios river basin are described and evaluated using GIS – the Revised Universal Soil Loss Equation and the Gavrilovič method. Implementing the ArcGIS 10.2.1 programme, the necessary input data for these approaches were estimated using four different quantizations that were created using topographic maps, courtesy of the Greek Geographical Army Service. The results indicated that even though a high-resolution quantization is always preferred for more reliable results, when there is a lack of available data, coarser quantizations can also be used to extract similar estimations.