**2.3 Data processing**

#### **2.3.1 Topography**

To calculate slopes inclination, we used Digital elevation Model of Calvados with a grid resolution of 20 X 20 m. The high resolution of DEM is essential because it allows us to carry out a topographical analysis of a very high degree of accuracy. Claessens et al. (2005) shows that DEM resolutions influence the slope inclination distribution: the coarser resolutions underline a larger contribution of lower slope angles (smoothing the effect on the landscape topographical representation). This report is in particular validated while comparing 50 m and 25 m DEMs. For Calvados, slope values result from the local cell-to-cell slope, rather than using a smoothing multiple cell windows, as done in major GIS procedures. Slopes were classified into six classes. Their limits were defined starting from values determined by statistics treatments of the cell slopes (classification according to the geometric progression method) and values coming from the literature (Le Bissonnais et al*.*, 2002). In contrast to the latter, the slopes larger than 15% have been regrouped in one class because of the absence of major dissected relief.

The classes selected are as follows: [0-1%[; [1-2%[; [2-5%[; [5-10%[; [10-15%[; >=15%. Those are respectively corresponding to the levels of pressure 0, 1, 2, 3, 4, 5.
