 In this video I'm going to show two ways of selecting the area for your download of the SRTM tiles in VertExplorer. The easiest way is to just use this window and go to the area of your interest. So let's say I'm interested in some area here in the Alps that I zoom in. So it covers the whole study area. And what you can do then is to say here use map. See if I zoom out that it will put these four points of the polygon and then this extent is selected. And then you continue with the dialogue to download your tiles. Another way is to use a bounding box of a shape file like in the exercise. But then you need to know how to make a polygon and I'm going to show that in QGIS now. So here we have some area on the Alps and I want to define a simple polygon with the bounding box. Then I can click on this button, new shape file layer. You can also go here layer create layer shape file. You can also do other types but the VertExplorer accepts the shape file layer. And then you can give it the name, bounding box for example. And you indicate here that it's polygon. You give here the projection. We keep it on latitude longitude that's okay for now. And we keep everything as it is because it doesn't need any attributes so I do okay. Now we have an empty bounding box file and then I can start digitizing. Basically what you can do is toggle the editing and then start digitizing. For a bounding box we just need four points. When you have clicked the last point you click right to close it. And then we just do okay and there's our bounding box. We toggle off the editing, we click save and then our shape file is ready. The next step is that we need to save that and then we need to change it to a zip file. Okay there it is and then we can use that in VertExplorer. So I'm going to clear the coordinates here and I'm going to add here shape file. I choose here shape file, I select the file and there it's loaded and there we see our bounding box. So it's as easy as that. To estimate the right area you need to know a little bit about where the sources of your catchment are and where the outlet is. So that's how you determine the dimensions.