 Hello, in this video we are going to derive the stream network by calibrating the strahler orders because in reality not every pixel is a river and the strahler orders that we have calculated give an order to each pixel and we can calibrate it by comparing the strahler orders with the rivers in a reference map like OpenStreetMap. So we start with calculating different order thresholds. Let's calculate a boolean map with all strahler orders larger or equal than 5 and we can use an on-the-fly raster as a result because we're not going to keep the results of the intermediate calibration steps. You can already see that it has a lot of tiny streams that might not be there but let's style it with a palleted unique values renderer and remove all the values that we don't need and we only keep value one the boolean true and we only look at the OSM layer below and there we see that this has far too many streams and doesn't represent reality correctly. So let's do another one. Let's calculate strahler larger or equal than 6. Create the on-the-fly raster because this is just calibration. We only need temporary rasters. Click OK and copy the style from the previous one and switch off larger equal than 5 so you can see the difference. Now we have much less streams but still too many so let's try strahler order 8. Same procedure. Paste the style and now it has less streams and I check it and it seems to be the best result until now so I think I'll go with value 8 in this case. If you don't have an open-street map layer with rivers you can also compare it with satellite images from Google satellite for example. So now we can use map algebra to derive the river by using this threshold of 8. Go to the processing toolbox and we're going to create a raster with only ordinal value 8 because we only can do the conditions with rasters and not with value so I create with the spatial tool or ordinal raster with only value 8 and I use strahler as the mask layer so the resulting raster will have the same size as the strahler raster but will contain only value 8 in the ordinal data type. I call it ordinal 8 so here's a raster with only value 8 for each set. If I use pelleted unique values it will find that it has only value 8. Now I can use that in a condition. So I go to conditional and Boolean operators and I choose the tool comparison operators and I say if strahler is larger or equal than 8, the ordinal 8 raster, then it will be true for the river and false for everything that we don't consider the river network. I name the result channel stop map. Here I run it and the result should be exactly the same as our raster calculator for strahler larger or equal 8 but then in the PC raster format. So that's our channel network in the PC raster format but we would also like to see the strahler orders of that network. So I can use an if then tool and say if there are channels then give me for those pixels the strahler order and for the rest no data. I call that channel strahler. Run the tool and go to pelleted unique values to find out that it has values 8, 9, 10 as we can expect. So now the pixels of the river are also in strahler order numbers 8, 9, and 10. So in this video you've learned how to calibrate the strahler order raster to derive the rivers.