Calculating Density (Hotspot mapping) in QGIS

in this video I will be talking about density calculation so revelation of where is the concentration of something highest so we'll be looking at where the concentration of capitals the highest there's a situation of population the highest and in gugus toga these as heatmaps or more general Colonel densities and and I will also in as a supplement to these kernel density juice raster layers I will also look at how one can quantify these density concepts using grids or fishnet whatever you want to call miscalculation time so it's a dive into how this is done in qgs so our usual dataset European countries capitals non capitals each of these has a attribute column back population that's the daytime population against no haven't checked doesn't really matter for this purpose so let's start out by seeing you know we are a capital hung growing person that wants to live bear there's lots of capitals close by so let's say that beyond the type that you know though of weekend bagging a capital so we want capitals to be will see 200 kilometers so where is the concentration of capsules highest we are looking for in the range of 200 kilometers so this is one of the things about density it's really somewhat dangerous too because often we do not think that this range element is 200 kilometers I would if I look or entity of capitals way in the 10 kilometer with this will give me something if I say 200 he'll give me a completely different picture so density is really one of those tools where you read something about density you probably should be hmm we did again check what's going on and if you could use yourself tell you use of what you've done because all of these parameters will have a really severe infant on the result so basically are two that we will be looking at is this heat map so first situation we wanted s to look at capital so we won our heat map and say okay I want to look at my single animal by one so this was what I want so the one that is projected and I've asked me what what is the radius I'm interested in so in this case I'm interested in in being able to go for Buren trip so I'm looking at 200 kilometers it's not going to be a rust output so it will specify how big this output sells well in this case a thousand by Faust beetle is probably appropriate it can do a range of influencing that was it it can't do a weight I'm looking at population we will do that in a moment then it has this kernel shaped okay there are different kernel shapes to be honest look no up in Wikipedia I only use the quadratic which is a a cubic function so what did and what this does is that it decreases the influence as a cubic function of the distance bill I'll show you diagram oh the uniform motion uniform just means is it is it not within the search pages I'll use this uniform for this case the K is only for triangle and I'm ready to run so this is my map and what we have is that we have a heat map so somewhere there is six capitals within 200 kilometers so let's change the symbology to a single band this is its finest colors so and yes you can see that that is somewhere down here now you can find not less than six episodes of in a 200 kilometer distance all of our place being was at zero so that's the basic way of using it one of the characteristics of this uniform distribution is that you can see that many of the places thanks yeah we have the highest density at the first distance from these capitals here so it says they're here in the middle of nowhere this is where we have the highest density well it is true that if I was going to find a place to live oh go on holiday and I wanted to play fine where there was five episodes when 200 kilometers I should find somewhere in this area here that's correct but it doesn't really say oh this is where the concentration of capitals the highest concentration of population or whatever it says it's more a question about how many capitals is a access to from this point so if we really want this more entity consideration let's look at what I meant by these with this Colonel fun so I quote re is basically think of it as a soft someone dropping soft ice lots so what will do is that bill drop a lob here at one look this is a capital and then it's influence or the K as a function of its the distance to the location and we can then add all of these up these are made so that the sum in here the area size of this air is equal to whatever the counting is someone if it's one population if it is a population so there's some tricks in this to be aware of but it's a it's a really useful way of approaching the density concept if we go back to our lay air so okay this was fine but let men let's look at population so if we want to find where do we have the highest capital person density so in that case I wanna go back to my heat map I run it again on my capitals in the right direction yeah and I wanna get use by ranges of 200 kilometers and can use grid cells at our one kilometer by one kilometer I will add a mate cell so it has this max population [Music] and I will use a quadratic so it will be these blobs of software of soft eyes on top of each other so they'll add up and they'll be decaying unto this to under kilometer radius so let's run this instead okay so we have a map like this let's skip those capitals so this is our population density again this time it's not in number of episodes but number of capital living population oh and change it to a pseudo color and then just fit this one and yeah let's keep this range like this so here we can see that cost big towns like Paris London grid again here in this area here we find that then we have the population is high as here you compare this to our map from before it said that strictly speaking we have access to five capitals go into uh no kilometers here but if we look at the population you see that this is highest up here so there is a clear difference in what we're talking not only it's because they're comparing population to account but also the way that it finds where the concentration is the highest so instead of just using this uniform where it's just is a capital in or not in the 200 kilometers well looking at how far away it is to this kernel density or means new Kubik varies best pic of it as these sort of software flossy eyes things so our soft eyes i was thinking but so this is those standard tools and they are they really useful make a good at giving you a type of lindsay you can use in both way around you can say so how many episodes are level in search pages or you can look there is a density of population the highest it's the same - its new - different wordings the other approach that is also very common is to apply a grid of fish net over the mapping area and then do a summing up move in each of these cells now there is a tools or creating it in who is equal grid so I create a grid first so I want this to be a hexagon this for the fun of it grid extent is going to be the same as a layer that is going to be the same as my countries bye-bye spacing so I put space and move let's say in kilometers again and say it then to be 100 kilometers in each of these so they will be spaced moving 100 kilometers in each dimension there's going to be no overlap and I'm going to use this Lambert Oconee section and I'll run my grid generator here so to make this last deal with that covers my entire and a decedent like I do from something what we're going to do in the moment is that be going to take all our non capitals that we have this single part don't camp those better use them so all of these and we're going to count how many other in each of them and what is the total population we jump so this is basically a join we're going to join our non capitals to our bids but we can not to use it some attribute to do it on but location so there is a we go join so we have these joint attribute by location and join attribute by location summary well this won't do this I could use this one to write into V each urban area grid are you part of I'll use this one if I wanted to add negate then points to my greens and that's why I want to do in this case so I'll use a summary function my input is going to be my single part non capitals I I guess okay my grid going to be my target I think it's okay that they're not same projection I'm going to say they have to eat too sick so it's going to be inside it what do I want to do well basically I just want to take what gonna do this run in this one way around bid and single are non-capital there so Waitsfield I want to measure on this as much better I want to measure by population backs so what are they wrong as I mix these up so this is the one I want to join into that one and what I want to do it well I would like to count how many there are and I want to calculate the sum so I want to know how many non capital cities obligated places are there within each of the grids and I want to know what is the sum of the population in them so I think I'm ready to run so um I have a your grid chart grid down there bring it up if we don't buy roll grid so this one has dates in it I start out by filling up all of those new datum as they're always models up the supplies a ssin of it so I'll just start out by saying that if my count is has to be larger strictly larger than zero so that will filter out all of those where there are no non capitals or in there is once that is done I can go in and do a symbology on it so I'll change it to a radiated based on the sum of population and equal intervals equal count so that's fine probably 110 and I want this one no wrong so I've got a lot of things going on here's a desk those so we have or in each of our so on grid cell survive use my eye to this Witsell yeah it to say that da three one two three non camtonz inside it and you can see here where there is nothing as no capsules there and at the same time I have colored the open this so this is the sum of population in the grid cell so it does give us so what we could is we could compare it's not quite fair because one is camisoles ours non cap salsa and trying different things here but this is in many ways the same approach and there this one does so we are looking at counting but instead of counting and anything it is it simply counting how many summing up how many people live or in these done capsules in each of these grid cell so density is in in general a a dangerous to because it has this concept of instance in its calculation and you should always really be careful of what you are pointing because it's two really cool different things if you want to look at your uniform so that's if you want to count how many dab in your search pages or you want to use one of these quadrants so that is is soft ice lots that melt out on top of each other of these two different approaches that you can use either the density so she and the wages has immense influence on what you do in that way it is some how easier to accept this fishnet because here you can see the size of the unit that we accounting inside so although it's bit more coarse it in some ways is a bit more honest easier for the reader to understand what's going on so be careful reusing the density tools they can be tricky and I hope I have explained the problems here so that you can communicate safely about densities you liked the video and I hope to see you on our one

Channel: Geoinformatics

Views: 1,938

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Id: rG1WBYVa7Ps

Length: 19min 58sec (1198 seconds)

Published: Tue Apr 21 2020