The DTM is a topographic model of the bare Earth. It contains the elevation data of the terrain in a digital format modelled as a rectangular grid [20]. The DTM is mandatory and used for two main reasons. On the one hand, it is a useful visual aid for specialised users when defining a context. As such, they shall add a DTM and represent it on the same map where they draw the context. On the other hand, the DTM is used at a pre-processing stage whereby each discretisation cell is assigned a topo-graphic elevation and other relevant parameters for hydrodynamic simulation (see Mesh).