QGIS 3.10 BASICS - Lesson 2 - Base Maps

right so lesson two we're going to be looking at base mapping and these are the layers that you're going to use to draw over the top of this might be an Ordnance Survey map it may be the results of a topographic survey it might just be any any map that your client sends you that you want to include in your product and in your project and in your map either to help you create data or answer your final base map on the actual map that you're going to produce you can get some data online for free you can also go to websites that provide mapping services that actually sell base maps as well or like I said these might be maps that your clients just sent you over that you they've either produced or purchase themselves so the first thing we're going to do is go go and have a look at one of the websites that actually sells base mapping data and this is a map site this is one that I use never really used any others this is just the one that was showed to me a long time ago other ones are available but I've just basically stuck to what I've known generally prices are fairly fairly much pretty much the same and the types of data you can get from them are pretty much the same as well there are some specialist ones for things like lidar data but let's just take a look at this here so your mapping data may be something like a aerial photograph we've got all these are the different products in here some of them are gonna be completely pointless and because they are too high of a kind of to low resolution to be useful like the traditional kind of OS LUN Ranger map is I mean you could extract a site boundary from that but and the location of some buildings and some ponds here but it's not really too much use let's explore a map gain a bit more detail you've got some paths and some other areas mapped out in here left the map district that shows you things in a slightly different way this has got mapped out the kind of areas buildings woodland and roads and some water features open map local raster this is one of the mapping products that's actually available for free through Ordnance Survey and is possibly quite useful for large sites smaller sites maybe not so much but definitely on large sites this is the product that I generally purchased the most OS vector map data gives you a lot more detail on they're generally quite useful for for base mapping to overlay your map on top and also gives you some boundaries that are also useful for when you're creating your map the absolute can a gold standard is Ordnance Survey master map and it's also the most expensive this isn't it it's it's auto zooming so when i zoom in further you'll see that is the most detailed you've got kind of boundaries of vegetation types here you've got the kind of the corners of buildings nicely quite detailed it's basically the best possible one that you can use but it's also the most expensive so we'll take a look at some of the prices for these kind of products first of all we'll look at see this is the master map data for that area you paying nearly 300 pound which for a site of this size you probably doing the Phase one survey for cheaper than that for lookouts aerial imagery it's actually quite reasonable the prices for aerial photographs so for a twelve point five centimeter resolution so basically anything that measures twelve and a half centimeters on the ground you would be able to see that on your aerial photo just thirty thirty three thirty four pound if you don't need it that detailed it gets cheaper down to a meter resolution twelve pound fifty five meter resolution 10 pound but if you wanted their most accurate version 5282 which again for some sites may not be too much money depending on your client really if they're willing to pay for it obviously the bigger area that you're using the more expensive it's going to be if we look at the vector map raster believe that's in popular products du/dr map raster 1493 and that will give you something that majority of sites is actually fairly usable site yeah so I was talking about the open map theatres as well that's available through OS opendata they provide all different scales you can either select an individual grid reference square or you can select the whole con free and you download that I send you an email and then you just download it from the link it's free you do have to give them some details just because they monitor who's using the data should also mention that it's available in vector and raster and we'll take a quick look at that and what exactly that means in a second so if we go and have a look at some of that data I'll just open that project that we were that we've created earlier and so this is so data that I've downloaded previously from EMAP site it comes in two files one is the actual image and the other is a file that shows you exactly where that image is going to be positioned within your map so that's prettier referenced all you do with that has basically drag and drop it in I'm not going to do that because you'll be able to see then where this site is and this is from one of my actual active projects at the moment and that's not in the public domain so I'm not gonna not gonna actually bring that into the project but we'll have a look at this the data here so raster data is image data if we just open that image just in a normal image view we can see that it's just an image file - bitmap image the more you zoom the more blocky it gets so the individual mapping unit of a raster map is an individual pixel where a vector map it's actually files GIS files shape files and in those it contains all the instructions it needs to actually draw those shapes so I'll bring both sets of dirt around so all we need to drag and drop in here is the dot SHP files can become quite confusing because the group of files associated with any one layer is a shape file but there's also a dot SHP file as well but you know just need to bring in the dot s hp's well it's gonna be tricky for me to find any particular location on these so yeah we can see that these are essentially shapes there'll be instructions in terms of the coordinates of each of these points around the outside and then it basically just draws lines in between if we bring in the other type of layer the raster layer something weird will happen when I bring these in be an odd pop-up and I'm trying to figure out exactly why it's happening because it's only something that's happening recently and it doesn't quite recognize the coordinate reference system that these files are using so I'm just gonna cancel these and manually change the way manually changed the reference system to National Grid I'm gonna zoom to layer so you can see like the buildings here if we look at these buildings so these the the image files are displayed above the vectors at the moment so I'll just drop these down below and then we'll get the vectors drawing on top of them so you can see here with these with the vector layer you can zoom in as far as you want to go we're actually at one-to-one scale there so this is true to life-size and there's no change in how crisp that line is because it's drawing it every time we change the scale with the vector maps that same building looks okay a certain scale but as you zoom in it then gets blocky and that's the individual kind of a unit on of on a raster map is just a pixel of a certain color where put the vector back over the top of that and it's this clean crisp accurate line so that's that's the kind of pre geo-referenced files that you can get either for free or auto purchase let me find where the site is that we're working on I think it's down here that's our Park there it's falkland Park in South Manchester so say we have some files that have not been geo-referenced these may have been provided by the client or you may have got them from some other source just just as an example I am going to just take a screen print from here and you use this as Iran on geo-referenced map so the project here best Maps so that's it here it's basically just an image file if we let me get rid of this PowerPoint if we take that image and literally drag and drop it it will first ask what coordinate reference system you want to be using British National Grid and then it will appear in a default location which is zero zero on the British National Grid so if we zoom to that layer you can see that it's not where we want it to be if you look at the top corner here if we look at the coordinates here it's at anyway the top corner here is at the zero zero so it's in that's basically off the southwest coast of Devon Cornwall so not in the right place it's not in South Manchester so we can't just do it like that it needs to know where to position it correctly so gonna remove that layer we're going to be using the geo-referencer tool which you I believe is actually a plugin and it isn't loaded already it should appear on the raster toolbar if it doesn't appear there you need to go to plugins to manage and install plugins and it's this one here so if you type into your reference err he'll come up your reference orgy doll if you click on in the install plug-in if it isn't installed already and then you tick the box to have it displaying as well I can't remember honestly if it's installed already as part of the core package I can remember in the past that I've had to install it but going from different versions of QGIS it kind of saves your some of your settings and I can't figure out exactly where so I can't make this look like a complete fresh install like everyone else will be using but anyway click on geo-referencer we click on open raster we find our map that's green print con type apparently we give it our coordinate reference system and now we have that here so the whole point of what we're doing here is adding control points this these are the options here add control point delete or move control point is basically we add a point and then we give it coordinates for that particular location or if we have map that's already been geo-referenced we can line those points up together so if we zoom back to these layers our Park is down here so there's two options here you can see here obviously we've gotten sorry accidentally click there we've got common common locations here this corner where we met up with the road or say this building here these are common points on both maps so what you can do is either so well not either first point is left click create new point and then it'll give you this option either input the x and y coordinates remembering that he's a British National Grid or you can click here from canvas so if we were going to input the coordinates wouldn't even we would need to know what exactly they are if we go back to where we got this map from you've got a coordinate readout down the bottom here of the X&Y coordinates of the numerical grid British national grid coordinates and also the Alpha numerical coordinates as well so if we go up to this top corner here and hover over our chosen point just here we can see now in the bottom corner that'll give us the grid reference what we do with that then is go back into here and type these in I'm just gonna the other option click from map canvas and click here and click ok so that gives us our first point I've got it so it pops up with this yellow box showing the actual grid reference you can you can Adam make adjustments so that in here you can turn them on and offshore IDs and show coordinates if you want to that's just a personal preference so another common point would be maybe in the road here corner you basically wanna kind of have sort of like four corners worth of points again you can either if you've got a base map already loaded in that's been pre dealer reference then you can just click on the common points if you haven't then you'd have to get the XY coordinates to actually input those and take a final point I'm eyeing up the corner of this woodland here that's common on both of these like Oh clay we can zoom out so we've got a good spread of points they're not all kind of clustered in one location they spread out kind of across the four corners of the map we then need to tell it what settings we're going to use to actually geo reference this how to transform it I'm not going to go into the differences of why we choose these different options I'm just giving you options that work well in most situations so choose helmet nearest neighbor we're working in British National Grid so it's British National Grid you will get a default file created in the same location as way your original image file was or you can click on three dots and change the location of that I'm just going to leave it here if your map has gone to be rotated if your original map isn't north-facing you may want to choose the option of you 0 for transparency because when it rotates you'll get this horrible black background in the original footprint of the map using that will turn it off but it will also wash out some parts of the map the other option got down here is loading QA yes QGIS when done click OK that won't start the geo reference and process you have to then click this button here which is start your reference and if you fresh start your reference and without going into the settings transformation settings it will prompt you to open that up so it dawn another point but if you press play now that's now into our map if we just minimize this and we'll check how accurate this is there's a couple of ways you can do that you can either make the make this more transparent drop the transparency down there so that's-- I should explain that if we go into properties then transparency and then drop that's lighter down press apply and then you can basically see how's that overlaid with the layer below it and we can see that's kind of that's quiet that's about right in this right location if you've got a vector map as well you could turn some of those points on so we can see that building it's kind of roughly in the right location those ponds the outline also kind of nearly match up with it as well I've done this fairly quickly so it's a little bit off it's not perfect but yeah once we've done that we can close the geo-referencer window and then that'll prompt you do ask if you want to save the ground control points click Save and then that's now fixed so if we go into our project folder we can see now we've got our original we've got our ground control points saved and we've also got a new modified map that is now geo-referenced so if we drag and drop drop that into the project if we remove this then it would basically just drop it back in the correct location without having to go through that same process again so another type of data that we may have to deal with and bring into the project again I'll just borrow that from magic I'm hoping that most people are familiar with this website it's Defra dot gov website called magic maps we can also get aerial photography from here as well so we can follow exactly the same process with this or slip the data they are other ways of getting aerial photography into your project but this is the only way I'm going to show you for the basic course you can do things like add plugins and add web-based layers where you can bring in sort of like Google Earth imagery or other sources but I'm just using this as an example on how did you reference so I'm not going to that today there are some complications when you're working with British national grid coordinates and also then overlaying something like Google Earth images because they work on two different coordinate reference systems and you need to make sure that they're projecting correctly between the two so again not going to go into that today but at least this is one method of allowing you to get aerial photos in I'm just gonna call that for tour partly because I always spell aerial wrong again same process opened your reference [Music] got the photo they're gonna call it British National Grid like I said before this also works for PDFs you can open a PDF through the geo-referencer window but a lot of the time that your reference doesn't like PDFs if they're large and complex it's better off if you convert that PDF into an image file not by screen print but actually using sort of like there's a lot of free websites that will convert a PDF into a image for you or if you've got access to something some of the old Adobe tools some of the Adobe programs will convert over for you as well but it's it's usually best to work on an image rather than a PDF for PDFs can work but what I found is if you've got a large site and it's a large complicated PDF you will occasionally get slowdowns and crashes of qgis or best to work with imaging so again with this you've got two options you can either find common points or you can find actual coordinates with with things like maps you're not always gonna get common points as crisp as you would with a Ordnance Survey base map sometimes it's because the angle of the image so with a building sometimes it's unclear if it's the edge of the foot if it's the edge of the roof or if it's the edge of the actual footprint of the building and that can kind of give you inaccuracies or where you've got a boundary it may be covered with trees trees are actually a really good a good way of do referencing things because it's usually a nice little kind of discrete point that you can find common on your map and also your original source a so here I'm gonna let's go through using coordinates actually so let's find some good common points we've got some kind of white object here so the tricky thing is now as soon as I move my mouse off here the coordinates in the bottom right corner are going to disappear so I'm gonna take a print screen come into this map it was this white object here I need to open paint to get that map pasted so we've got our coordinates down in the bottom here so this is a very usually I'm working on two screens so it's not usually this fiddly right so well this is gonna be a pain to do three eight five two two eight three eight five two two eight three nine two or three or three nine two why so then you've got your common points football pitch could be useful pick out like a center point or a corner actually what I'm gonna do is make this only half screen so then I can have it on the other side of the screen yesterday a reference a bit down the bottom corner so from magic up on the other side of the screen right common points copyrights annoyed I'm gonna go for a little a little this is the the way caused by the goalkeeper obviously it's not zooming on here as it is on the magic site because we've taken a screenshot where magic it's it's showing a different level of zoom each time we actually zoom in so hover over here hoping I'll cover up here that I'll update and I can just start typing yeah we need two more points I think I'll probably use one of the cars down here my cost economists the windscreen of the white car only actually it's a white band this is a real pain when you don't have two screens you could write it down on a piece of paper one final point from this side of the site and we'll just we'll use one of these trees I did say that trees were useful for getting dereferencing points or even where these paths intersect I'll use the PAP intersection three eight one four six sorry guys this bit is a little bit dull but at least it shows you the full process both different ways of doing it so like okay again we have these four control points usually the more control points the more accurate control points the more accurate your geo references are going to be if you've got an image that is warped in any way that isn't quite right there are other transformation settings you can use to have a kind of local local warping in the map so you can put more points in a particular location so I'll kind of stretch those local points out where generally the this way of doing it helmet nearest neighbor that just kind of stretches the whole canvas out and an even kind of way it's because we're taking this from somewhere we know that is displaying this in the correct British national grid format we know that when we overlay this on to our map it's it only needs to be stretched and repositioned in a even way anyway let's press play that's just double check that by again we can have the buildings overlaid on top so they kind of match up with buildings we can stick other things like roads on surface water woodland and they do over there quite nicely in those locations so that's that's this well let's finish this off properly we need to close the geo-referencer window and save the control points so we should go a little bit into the anatomy of a project at this point and look at all the files that have been created there was as a result of saving this project so far so if we so an actual project file that's what's created it's just the q GS file in the base maps we brought in the photo and we brought in the screen Pring and that's then created point files for both of those and then create a modified version which is like a geo-reference version of them and that's what we have so far so at this point we will so basically you can you can completely delete this project at this point so you could delete this file and it wouldn't affect these files so a project file holds all of the formatting information for all the layers that you are including in a project and the locations of those layers but it doesn't actually contain the data for those files so it doesn't contain the image for the images or later when we come to creating features in a shapefile it won't contain these individual files these are separate separate files you load them into a project the project remembers where these are and contains information about how to format these but the actual shape files themselves and all the data on how to draw the shapes are contained within these files here so each one of these shape files will go by name so then it will group them you can see this four different files here sometimes you get more than that but it is a grouping of files for each of these layers that we've got over here rather than just a single file and the data is held within these files rather than the project file I hope that's clear and I think that is now time to move on to our next lesson

Channel: QGIS for Ecologists

Views: 12,178

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Id: _t6ee-cvyyw

Length: 38min 59sec (2339 seconds)

Published: Sat Mar 28 2020