The slope properties of terrain may be calculated in a variety of ways. Slope maps are used for the purposes of terrain evaluation in the context of landing and rover safety. Slope maps are typically calculated at a specific length scale or 'baseline', specified according to particular mission requirements (e.g. radar navigation during EDL, or rover performance).
As specified in the landing site Users Manual surface slopes relevant to ExoMars 2020 are calculated at baselines of 2, 7, 330 and 2000 m.
A relevant method of calculation for slope maps is the 'Maximum Adirectional Slope', presented by Masarotto et al. (2011), which determines the maximum slope from every point in a terrain model at a baseline distance. This presents a 'worst case' metric by which to judge slope hazard, though methods such as 'steepest neighbour' (available in common GIS packages) may be similarly representative if the terrain model is first resampled to the desired baseline.