Tutorial: Stream and Catchment Delineation

5. Create a Subset of the DEM

In order to reduce the calculation time of the algorithms, we will subset (or clip) the raster layer to the boundingbox polygon.

1. Now, from the main menu select Raster | Extraction | Clip Raster by Mask Layer.

2. In the Clip Raster by Mask Layer dialog, choose dem_reprojected for the Input layer. For Mask Layer, choose boundingbox. Check the box to Keep resolution of input raster and keep the defaults for the other options. Choose dem_subset for the Clipped (mask) output and click Run. Click Close when done.

Often you'll not have a bounding box shapefile. In that case you can choose Raster | Extraction | Clip Raster by Extent. Then you can drag a box in the Map Canvas and use that for clipping. While using that, make sure your on-the-fly reprojection is similar to the layer that you want to clip, because the map canvas coordinates are used by the algorithm.

3. Now you can remove dem_reprojected from the layers list as we have done before for other layers that are no longer needed.

Watch this video to check the steps in this section: