 Hello, this is Hans van der Kraas, senior lecturer at IHE Delft Institute for Water Education. In this video I'm going to explain a bit about the spread or proximity functions from PCRuster in QGIS. There are different tools available for that. I'll focus on spread, spread max and spread max zone in this video, the ones that are related to water will be explained in another video. That is the ordinary proximity tool and it needs an initial friction layer and a friction layer that impacts the distance. If you want just Euclidean distance then you keep the initial friction at 0 and the friction layer at 1 and they are spatial so we need to create them with the spatial tool. So I create the initial friction of 0 by choosing a value of 0, making that a scalar and saving it as initial friction, maybe before so here I can replace it, replacements are not really recommended if they are different because it doesn't always overwrite, I've seen. Make another layer with a value of 1 for each cell and that will be the friction layer. So with initial friction of 0 and friction of 1 you can have just the distances reported in the spread tool. I use here the industry pixels as the points from which we want to propagate the distance and initial friction and the friction layers and I write the output to indist and then I run it. And now I get for each pixel the distance to the industry cells, so to calculate it from the zeros to the non-zeros and we only had the ones here which are true for industry explained in a previous video. And if we want areas that are further than 300 meters from industry, we can use the raster calculator and we say indist larger equal to 300, so here again you see that you can use PC raster results combined in other tools in QGIS which is Boolean, it's true for cells that are further than 300 meters and false for cells that are less than 300 meters. If we are interested in a maximum distance we can use spread max which will calculate the distances to a maximum value that we have specified. So here I choose the roads, add initial friction and friction and I want a maximum distance of 150 meters called the output spread max and when I run it I get a layer that has the distances until 150 meters and which is further gets value zero. Often however we want the cells within a maximum distance to have the same value as the cells from which the distance is calculated then we use spread max zone. So in this case we use the roads map as an input and we do the same calculation and when we run it we instead get now the value of one that was for the roads and the value of zero for the areas that are further than the 150 meter threshold. If I style it as a Boolean here we see the result of our buffer. Now we can also do this for the houses layer to determine which areas are within 150 meters from the houses but in a previous video we have used a TIFF and we cannot use TIFF files as an input. So I'm going to reclassify the buildings layer again to get the houses out of it but I'm going to use a lookup table where I say class 0 remains 0, 1, that of houses will be 1 and then from should be 2 to the maximum value will also be Boolean 0. So as easy with these lookup tables I can simply reclassify the buildings layer to get the houses out of it in the PCRuster format. I use lookup to correct one. I'll put this a Boolean, houses and no houses so I call it isHouses, run it, there you have the result and then I can use the spread max zone tool again to calculate the distances. IsHouses input and then the friction layers within 150 meters and I get the value of houses for all the cells that are within 150 meters and 0 for outside. Let's try it as a Boolean and there we see the result. So it's very easy to do all these distance analysis with these tools and you can combine it with the other tools available in QGIS.