So, by the end of my previous post on this topic, I’d used Ordnance Survey OpenData products in QGIS to produce a nice smooth depiction of the topography of Ordnance Survey grid square NG, tinted to show height and shaded to show relief. It looked like this:
A detail, showing the region around the mountain Blaven, on the Isle of Skye, looked like this:
The next step is to add some contour lines, to give an extra impression of the relief. Last time, I described how I’d downloaded the OS Terrain 50 vector dataset, in the form of ESRI files, and unzipped its data folder inside a folder on my hard drive named OS Terrain 50 (ESRI), so as to keep it separate from the Terrain 50 Grid dataset I used last time. This data folder contains a host of sub-folders with two-letter names, each of them corresponding to one of the OS’s 100km grid squares (shown at left), and each sub-folder containing a set of anything up to a hundred zip files of its own, each containing contour and spot-height data for a 10-kilometre square of terrain. Once these are unzipped, you find the contour data in files with “line” in their names, and the spot-height data in files with names containing the word “point”. There are multiple different files for each 10-kilometre square, but the important ones have the extension .shp—shape files. The rest contain supporting data that QGIS will handle automatically.
To get contours for the whole NG square, I loaded all the “line” shape files from the ng sub-folder. I find the easiest way to do this is to use the Browser window in QGIS to navigate to the appropriate folder, and then to enter “*line.shp” into the filter tool (brought up by clicking on the little picture of a filter funnel in the toolbar of the Browser window). This brings up a list of only the necessary files. I select all of them, right-click, and choose Add Selected Layer(s) to Canvas.
The result looks something like this:
It resembles some sort of mad quilting project, because QGIS has coloured the contours from each 10-kilometre square differently. We need to combine these into a single file, so that they can be consistently coloured. From the main toolbar, select Vector/Data Management Tools/Merge Vector Layers…. In “Input Layers” select the names of all the *line.shp files. For the “Destination CRS” choose the option that includes “OSGB36”, and under “Merged” provide a memorable name for the output file.
Once you have the new merged layer loaded, you can discard all the individual tiles from which it was derived. Now we just need to apply the default style from the OS’s cartographic stylesheets. Double-click on the name of the merged contour layer in the Layers window to bring up its Layer Properties dialogue box. Click on Style/Load Style at lower left of this dialogue. Navigate to the correct style definition file in the Terrain 50 stylesheets folder (I described how to create this last time). There are a lot of nested folders, but the file we want is OS-Terrain-50-stylesheets-master/ESRI Shapefile contour stylesheets/QGIS Stylesheets (QML)/line.qml. Once applied, the final result looks like this:
It’s a bit cluttered at this scale, because the Ordnance Survey style for contours is to plot them at a constant width, irrespective of scale, which makes sense. Zooming in on Blaven, we find things look more reasonable:
The OS contours include three classes—meanHighWater and meanLowWater, which appear along the coast and are tinted blue; and ordinary, which marks land elevations and which defaults to a rather garish russet. I toned this last one down a little by modifying its properties in the Layer Properties dialogue box, under “Symbology”, like this:
I’ve set it to a browner shade, and wound its opacity down to 50%. In general, I’ve tweaked most of the OS’s default styles to suit my own purposes and tastes. (By the way, you can label the contours with their heights by going to “Labels” in the Layers Property dialogue, replacing No Labels with Single Labels and then setting “Label With” to PROP_VALUE, which is the variable in which the dataset stores the height of each contour. I prefer to reduce the clutter and keep labels turned off—for the maps I’m making I just want the contours to indicate the shape of the landform.)
Now to add some more geographical features. The meanLowWater contour looks a little odd at present, sitting in the sea, but in the OpenMap – Local dataset (which I described downloading last time), the OS provides a shape file called *Foreshore.shp, which fills the space between high and low water. In this case the necessary file is NG_Foreshore.shp, which is stored in a folder called OS OpenMap Local (ESRI Shape File) NG/data, along with all the other shape files I’m going to be using in this post. You can add it as a layer using the main toolbar Layer/Add Layer/Add Vector Layer…, and then navigating to the right folder.
While we’re there, we can add surface water features, in the form of NG_SurfaceWater_Line.shp and NG_SurfaceWater_Area.shp. NG_Woodland.shp adds areas of forest. All of these will load with random colours assigned by QGIS, and need to have styles applied from the OS OpenMap – Local stylesheets, which I described downloading last time. The styles we want are installed to your hard drive in a folder called OS-OpenMap-Local-stylesheets-master/ESRI Shapefile stylesheets/QGIS stylesheets (QML)/Full colour style. They have descriptive names that match the shape files—Foreshore.qml and so on.
Here’s what Blaven looks like with those geographical features added, and after a little tweaking to the default OS styles:
It’s becoming important to have all these layers in the right order—you can see the order they’re stacked in in the Layers window, and you can drag them up and down the sequence to achieve the right effect. I have Foreshore sitting immediately on top of TidalWater, and just below the contour layer. SurfaceWater features are on top of the contour layer—I think rivers look better without contours crossing them. Woodland has had special treatment. I’ve turned its opacity down to 30%, so the topographic tints can show through slightly, and slipped it below the Hillshade layer, so the forest areas look like they’re following the slope of the land.
With the natural environment properly depicted, I’m now going to add NG_Building.shp and NG_Road.shp. Again, these can be styled from the OS stylesheet, and then tweaked according to taste. But there’s a twist with the styles for roads. Not only does the road style file contain multiple different styles according to whether we’re dealing with a motorway, an A-road or a track, there are actually three separate style files for roads—RoadCase.qml, RoadFill.qml and RoadCentreLine.qml. These are designed to stack one on top of the other, as three separate layers, producing (respectively) a dark edge, a coloured middle, and any centre line required to symbolize dual carriageways. All of them use exactly the same shape file. So, having loaded NG_Road.shp, right-click on its name in the Layers window, and select Duplicate Layer. Then do the same again. Now you have three copies of the Roads layer. Right-click on each, choose Rename Layer, and give it a name corresponding to the style you’re going to apply. Then add the OS styles. Here’s the order everything should appear in in the Layers window:
And here’s how it all looks after I’ve slightly tweaked the OS styles:
There are other features in the OpenMap – Local shape dataset, but none of them are relevant to the image I’m working on here. You can add roundabouts (two styles are provided, one for the dark outline and one for a coloured fill, so the layer needs to be duplicated). There are railway tracks, railway stations, and road and rail tunnels, all of which are necessary when producing maps of other areas. (The depicted railway tracks are broken where they pass under bridges, so you should put the railway layer on top of your road layers.) A number of other more specialized features are also available—take a look at the Ordnance Survey’s OpenMap – Local product guide (1.7MB pdf) for more detail.
Next time, I’m going to write about how to add and format place names.
One thought on “Ordnance Survey OpenData In QGIS 3: Part 2”
That’s much too techie for me A good thing though.