Interactive Terrain Mapping in QGIS

During last year's winter break I did a little animation of Arctic sea ice, which eventually ended up being shown in slightly modified format in Svalbard Museum - and they even sent me a nice hat for my efforts. This year's spare time project was to look a bit more at terrain mapping in QGIS, with a purpose. Since I'm a Highlander in exile I dream of the hills quite a lot, and the mountains in particular. If you follow mountain weather reports for the Highlands, you'll hear of fairly regular avalanches. They may not have the ferocity of avalanches elsewhere in the world, but they can be deadly. The Scottish Avalanche Information Service do a great job of recording, documenting, mapping and educating here so I thought I'd add this data to some 3D interactives using Minoru Akagi's Qgis2threejs QGIS plugin and Ordnance Survey Open Data. If that sounds like gobbledygook to you, never mind - just look at the little animation below to see one of the outputs. The red dots are the locations of recorded avalanches since 1991. You can also play around with it in your web browser - it's quite good fun.

Avalanche data is from the Scottish Avalanche Information Service

I extracted the avalanche data from the SAIS webmap and just plotted the locations in QGIS. I decided to focus on an area I know relatively well - the Cairngorm mountain area. It's not high by world standards, at 1,245m/4,085 feet (6th highest in the UK), but at 57 degrees north and nothing much protecting it from the fierce winter weather, conditions up there can be extreme. In fact, I remember growing up sitting many times on the old chairlift as it swung in the wind! Not for the faint hearted. Anyway, as is the way with these things, the area I wanted to look at was split between map tiles, as you can see below in this QGIS screenshot.

I think there must be a name for the law of split map tiles

Methods-wise, I just patched together a few map tiles, clipped out the area I wanted to focus on, overlaid the avalanche location data, generated a hillshade with an azimuth of 180 and elevation of 27 (to simulate shadows at noon on 26 December), and then added some Ordnance Survey map tile data on top of it. I also did a version with Google satellite imagery, just to see what kind of result I could get. I've posted a little gif of the satellite version below, followed by more of the images. You can also play around with a smaller version of this in your web browser. It should also work on phones, but you might have to use three fingers to pan around.

This uses Google satellite imagery - interactive here

What you'll see below in the next five images are just screenshots from the final interactive from my web browser. You should see them in larger size if you click on them. I've modified some of the settings slightly but basically it's quite an easy thing to do in QGIS with the Qgis2threejs plugin. The updated document on this (18 Oct 2016) is also available in a single, handy pdf. If you want to use this tool, you'll find lots of useful tips in here.

Full view of the final interactive - looking north

Focused on Loch Avon (pronounced Loch A'an) 

This shows the main areas of avalanche activity in one view 

This is a view with the Lairig Ghru pass in the foreground

Another more vertical view of the southern part of the area

I like the effect here with the hillshade layer providing some sense of depth and shadow. There is no vertical exaggeration here and in the interactive version you can zoom in quite far before it becomes pixellated. I also wanted to see what kind of quality I could get by adding in a Google satellite layer and then exporting that. For this, I used the OpenLayers plugin in QGIS (though QuickMapServices is also really good for this). The final version was pretty big as I exported at a high resolution, but here are some snapshots.

The full view of the satellite version - click to enlarge

Loch Etchachan - watch this video!

A different view, showing a cluster of recorded avalanches

The resolution here is actually quite good

This is a view from 'over the back' of the ski area

One final overview image, just for completeness

As I said above, I also did a little extract of this focusing on a smaller area around Loch Avon. The satellite imagery changes part way along the loch but it's still quite pleasing. The interactive version works pretty well in the browser and the image quality here is also pretty good (I exported this at 200% in the Qgis2threejs settings).

Loch Avon - a nice little video from March 2016

It's not always winter here - take a look

Along the way, I almost forgot why I started to map this - the purpose was to plot some interesting and important data on top of the terrain in order to try to understand more about which areas are particularly prone to avalanches. Along the way, I learned more about Mike Spencer's snow hydrology research and PhD (more on that here) and found out some stuff that will help me update my teaching material on this topic. I did begin to look at the Ben Nevis area as well (below), but I decided to focus on the Cairngorms instead this time.

25 years of avalanche locations (red dots) for the Nevis Range

That's all for now. Thanks to the kind of data collected by the SAIS, Ordnance Survey Open Data, and great tools like QGIS and Qgis2threejs, it's becoming much easier to explore, analyse, visualise and understand important datasets. That is kind of what I was attempting here, as a little holiday experiment.

Thanks for reading.


Map data: Contains OS data © Crown copyright and database right 2016

D3 Charts in QGIS Print Composer

This post is about how to make charts created in d3.js appear in QGIS and how to make them work in the Print Composer so that you can export them with your maps. It's inspired by the recent publication of a new QGIS plugin which allows you to create one kind of D3 chart within QGIS. For this example, I'm using Motor Vehicle Collisons data from NYPD, because the QGIS plugin here needs data with time stamps in it and this fits the bill. Also, it's an interesting dataset because it's a good example of something where time and place are important. Collisions are closely tied to certain locations (e.g. intersections) but they are also more likely to happen at certain times (e.g. 8am, 6pm). First up, here's a little visual of lower Manhattan collisions by time of day, using the whole of 2015 - don't worry, there aren't that many collisions in a single day, even in NYC.

Crash, bang, wallop

Okay, so we have a gif with lots of flashing dots, which isn't very helpful. But it does tell a very basic and obvious story. What if we wanted to put a static map in the Print Composer beside a radar chart showing collisions by time of day? That's where the D3 Circular Date/Time Heatmap plugin comes in handy. In QGIS, just search for D3 via Plugins... Manage and Install Plugins to find it and install. Once you've done this, you'll see the little chart icon in your toolbar area. To make it work, the best thing you can do is follow the original tutorial, which uses 2006 Chicago Crime data. You'll see in my example below for the NYPD data that I've set the chart to show day of week and hour of day so that I can get a sense of the time pattern associated with collisions.

Note: this plugin produces circular charts only

Once you hit OK on the plugin, you'll get a D3 output page which will render in your web browser, after you tell it where to save the output files to. When you do this, you'll see three new files in your designated folder, as below.

Nice small file sizes with D3 here

Now you might want to add this chart next to a map of collisions in your Print Composer in QGIS. You can do this quite easily. First of all, you just need to get things ready by positioning the map output as you wish. In this case, I've gone for a landscape layout and I have a little Manhattan collision map on the left, showing only some collisions and the circle chart on the right. Here's a screenshot of my Print Composer showing that I've just added the D3 chart using the Add HTML Frame button. I've just told QGIS where I saved the chart by pointing it to the location on my computer where I saved the new chart, but you can paste in the original code in the box below that if you wish.

Still looks pretty messy, but you get the idea

In the example above, I've changed some of the original defaults in relation to fonts and so on, just for my own benefit. You can also go in to the html and tweak whatever you want - in fact it's quite a good way of getting used to how it works if you've never done it before. Then you might want to export the map at a decent resolution. This is what I've done in the example below, which is only for test purposes because it's not a finished map - I'm just adding it here so you can see what the D3 chart looks like from an exported Print Composer layout.

Just to demonstrate the resolution - click to enlarge

A little close up on the chart, just to highlight the quality

From here on in, it's just a case of experimenting more and more until you get what you want. There are lots of different ways to generate D3 charts and other output, including online tools such as Raw or even learning a bit of D3 yourself.

Finally, take care when crossing the street in NYC.

Notes: if you're looking for a QGIS plugin that will turn your whole map into D3 and make it interactive, look no further than Simon Benten's D3 Map Renderer, which is really cool. This example I've shown today is really very basic, but it shows you how to get some D3 into your QGIS projects, should you want to. For the most advanced, beautiful examples, check out Jason Davies and Mike Bostock. You'll sometimes see it written D3, D3.js, d3.js or just d3 - it's all the same thing. I prefer D3. For nice practical examples of D3 in the wild, check out the Financial Times page - with John Burn-Murdoch and Alan Smith really leading the way here.