 Hello, this is Hans van der Kost, Senior Lecturer at IHG Delft Institute for Water Education. In this video I'm going to show you first how to iteratively clip a raster using several polygons and secondly how to do that in the graphical modeler. In this example we use a digital elevation model as a raster and we use a subcatchment polygon layer as the polygons that we want to use to clip the raster with. So in the raster menu we can find under extraction clip raster by mask layer. We can choose the DEM as the input layer, the subcatchments, polygons as the mask layer and there we have this option, iterate over this layer and then the outputs will be generated for each polygon separately. We can assign a no data value, check keep resolution of the input raster and here we don't give an output name because it will iterate and give it automatically. So here we see that it does it automatically, that saves a lot of time. So the result is there for each subcatchment polygon. Now I'm going to demonstrate how to do that in the graphical modeler. Let's create a new model and it's important that you use the vector features input option and not the vector layer one. Only when you choose the vector features you can choose the iteration option. So subcatchment polygons, geometry type polygon and we add a raster layer, make it generic for any input raster layer, you can later use it to clip a land cover or other features. Then we use that clip raster by mask layer tool, choose the input raster and then the subcatchment polygons and this resembles of course the tool that we used before. So we add the no data value and then it would be nice to see what happens if we calculate something from that output because it will be iterated. So let's calculate the slope. So normally if we don't iterate we'll get one slope map, we indicate that the output name is the slope layer, so the outputs indicated in green, inputs in yellow and then the tools are in white. Let's give our tool a name and a group to which it should belong in the toolbox and we save our model. So we find it here, let me first remove the previous outputs that were generated. When we run it we can choose the input raster layer, the DEM, the subcatchment polygons and there I can check that button to iterate and it will perform our analysis for each subcatchment. And there we have the slope for each subcatchment. So that's a very useful tool if you want to iterate over polygons and apply some analysis on each polygon separately. If you've enjoyed the video please subscribe to my YouTube channel and receive updates on new videos and for more free materials you can go to the IHG Delft OpenCourseWare at GISOpenCourseWare.org