QGIS 3 Lesson 2 Using slope analysis tools for rasters in qgis

hi i'm tim albright and welcome to d-mad marine mammal research association's third course this is lesson two and today we're going to be looking at slope analysis please remember to keep liking subscribing and most importantly sharing these videos so that we can reach as many people as possible okay so in this lesson i've just got our raster up again um the only difference between this raster and the one that you were using is that we set a zero value on the previous raster if you want to do that it's not really that important but you go to transparency and we'll just set the additional new data value um and today we're going to look at something called uh sleep analysis and slope analysis is really quite a simple process once we've got our dem uh but actually quite an underutilized process in my opinion um knowing how steeper slope is can be really important people said that they wanted some more marine biology examples well if we're designing our survey and we're looking at a survey area we know that there's certain animals certain species of dolphin for example research dolphin that really like uh slopes steep slopes um and steep drop-offs and so we can find out where these steep slopes are we're going to be using a terrestrial example today but there's no reason it can't be applied to our uh our elevation model of the sea floor so exactly the same sort of thing um and in this course i'm going to show you where things go wrong as well um hopefully this has helped you if you run into similar situations um so in a couple of videos you'll notice that i'm deliberately making mistakes to show you these say for example in this video i'm going to go to raster analysis and slope and i've got my complete raster file here i just hit run and you will notice i get this really horrible uh output raster which is uh running from zero to 90 degrees only 0.90 so it's uh just binary and it's telling me that um everything that's flat is zero well everything where there's a zero value is zero effectively and everything else is a slope of 90 degrees which basically means that the slope is vertically upwards so zero would be flat and 90 degrees is vertically upwards in this case um and obviously montenegro isn't a series of vertical slopes so this is incorrect and the reason for that and actually this is my fault is that um our raster wasn't projected into etm um so what we need to do is we need to just uh save this layer so go to export and save us and i'm just going to save it as raster not taster utm 34 and then just come in here and make sure we find our utm 34. if it's utm 34 because it's montenegro you'll have to find the etm area for whatever reason your working in um a quick search engine will tell you that if your utm zone doesn't appear in this list you can just click this button here and i'll take you to it so i've done that and i've brought in my utm zane and it's you'll see it's twisted very slightly um that's not a problem you'll notice that if we untick then our rasters still match um quite nicely now as i said it's very simple you just go to raster analysis and go to sleep and this time um yeah this time we can just click run i'm going to save it this time so just come down to my slave analysis i'm just going to save over my file so click yes you won't have that option because you've not created one then i'm going to click run and you'll see now i get this far more useful raster i'll just remove the one underneath i guess far more useful raster which shows me that i've got these really steep edges here and i've got a really steep ridge here and a really steep ridge here um we've got this sort of white line around the outside just because we've got no data around the outside so uh qgis is going from zero to whatever data value this is so we just need to be aware of that um again if you want to turn [Music] this black around the outside you just have to set the transparency value so i'm going to hit zero click apply and we'll get the same thing and that will get rid of that white line but i mean you don't have to get rid of it but it's just something that we need to be aware of that we do have um zero data outside of our montenegro country file in the example we've been using um and now you can see we've sort of got this uh yeah we've still got these darker areas which are very flat you can see this is uh all the area around the lake that we constantly refer to um so it makes sense that's flux it's a bit of a catchment zone um and then we have these areas which are the the mountainous areas we sort of looked at in the last lesson um and you can see that actually these are these are really quite steep areas similarly coming away from the bay you can see we've got these really steep areas and this little ridge down here so like i said that can be really useful because there are certain animals that really like being around the slope and yeah it can be really useful because we can if we if we want to be doing a survey and we only have limited resources which i unfortunately we find ourselves a lot in marine biology then uh we can look at certain areas where we have uh suspicions that there might be a greater chance of these animals in greater detail and therefore um yeah therefore we can sort of um use our resources the most effectively okay i hope you found that you lesson useful and i'll see in the next one you

Channel: DMAD Marine Mammals Research Association

Views: 1,168

Rating: 5 out of 5

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Id: So8g0GGb110

Length: 7min 29sec (449 seconds)

Published: Tue May 19 2020