A Digital Terrain Model (DTM) is a bare earth model that is derived by removing buildings from the original Digital Surface Model (DSM).  Buildings and trenches are removed by analyzing local regions where the surface changes rapidly, removing those sections of the DSM and backfilling with neighborhood data.  This process is fully automated and retains most of the original resolution and accuracy of the source DSM.  

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The figure below shows the DSM and DTM for downtown Riyadh.

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