Saturday, 3 August 2019

Playing around with shaded relief maps

Last summer I was playing around with maps of where ships go, but this summer I'm back on land with some shaded relief maps, just for fun - and also a bit of an experiment in styling, labelling and all that. This is all very simple: I took a single tile from NASA's SRTM 1-arc second dataset (basically a map tile with a resolution of about 30 metres, covering a rectangular area about 110km north to south and 60km east to west). This data was captured in 2000 by the Space Shuttle Endeavour from 233km above the earth. The easiest way to download it is using Derek Watkins' 30-meter SRTM Elevation Tile Downloader. Anyway, enough of this for now, here's one of the final maps, which I'll explain below alongside more maps and technical information and stuff about the area I've mapped.

This is the 'single malt' version

The map you see above is of a single SRTM 30 metre tile - NG57004 - and I did it all in QGIS 3.8, no other software involved. There are a few layers here with different blend modes and transparencies plus some basic labelling that I added manually. The area itself is more or less a bit of the Cairngorms plus Speyside in the north of Scotland and is just to the south east of where I grew up so I'm very familiar with it, and if you like Scotch whisky or shortbread you might be as well.

Movie stars, whisky and shortbread

This area is world-famous for whisky production and indeed the Speyside area is one of the five whisky regions of Scotland. It's also where I went for school trips to places like Boat of Garten and Nethy Bridge. If you're into this kind of thing you'll also notice that some of the place names relate to famous Scotch whiskies, including Glenlivet, Knockando and Dallas (as in Dallas Dhu single malt, which actually comes from just outside of Forres, nearby). You may notice in the bottom right corner of the map some places associated with the royal family - including Braemar and Crathie. You might also see Aberlour in the north east portion of the map and that's where Walkers shortbread comes from - one of Scotland's big food exports and which I have seen for sale in airports and shopping malls from LA to Beijing.

You'll find polar bears down in Kincraig and even a bit of surfing at Lossiemouth beach (cold water! I've tried it). But I mainly chose this area because of the lumps and bumps of the Cairngorms - not very high elevation-wise but at 57 degrees north and with five of the highest six mountains in the UK (named on the map) this part of Scotland can be a very harsh environment - though also extremely beautiful. I've shared some more traditionally-shaded versions below but this first one above is deliberately a bit different, since I have gone with something close to a single malt whisky colour scheme. See below for the a slightly more exotic one.

A bit exotic but I like this version

Growing up, I also used to take the bus from Inverness, hire some skis and go skiing at Cairngorm Mountain and remember feeling like I was suffering from severe frostbite on the old 1960s chairlift (in the days when sledges and giant inner tubes were not uncommon and it was all a bit hot tube time machine fashion-wise). Anyway, if you like 50 mile an hour crosswinds, boilerplate ice and zero visibility conditions the Cairngorms are the place to be. If you've visited in summer during midgie season then you'll definitely prefer the former (seriously, see this video).

Right, back to the maps - the next three are as follows: a slightly subtler version of the original above, then a couple more traditional shaded reliefs - one in purple shades then one in orange shades.

I was going for 'single malt' but might be burnt toffee

Some people prefer this kind of thing

This is a lot subtler but not as interesting I reckon

A few other things to say about the maps. I've added a couple of place names to the Tarbat peninsula to the north west of the map - they're not part of the area I wanted to map but I always like to know what's what. Plus Portmahomack is an interesting place and you pronounce it just as it's written (like Drumnadrochit!), unlike loads of places in the Highlands, such as Avoch, Kilravock, Ballachulish and many more. Oh, and Moray Firth is not 'Mo-ray' - it sounds just like 'Murray'.

I've also added a curvy 'Cairngorm Mountains' label and a smaller 'Monadhliath Mountains' label on the west side of the Spey - hopefully it doesn't stray too far north although I'm not 100% sure on what's considered the northern limit of this range.

I did do a version in a more traditional topographical style so I've posted this as well. Below that, you'll see one more version - in greyscale, just to complete the set.

Possibly a bit more realistic
This actually looks quite pleasing

I was just playing around with a bit of relief data here during some down time, and wanted to make a few maps that looked a bit different but were still recognisable as shaded reliefs. I could probably spend hundreds of hours on this if I wanted to get everything right. The underlying data is pretty good resolution (30m, roughly), better than the 50m resolution open data from Ordnance Survey. I do have access to the 5m resolution data but since it's not open I didn't use it this time, but it would give a lot better quality image. We do have 1m resolution Lidar data for small chunks of Scotland, so it's a shame the 5m Ordnance Survey data isn't yet open.

'What does this area look like on the ground', I hear you ask? Well a good chunk of the off-road stuff, including the Lairig Ghru and Ben Macdui is actually on Google streetview, and you can see a screenshot below.

If you're looking for some seriously fantastic NASA-related mapping, check out the amazing work of Joshua Stevens.

That's all for now. The original 300dpi maps are in this Dropbox folder, if you want a closer look.

All six in one

Technical notes: the elevation data you see on the map is released via NASA's Jet Propulsion Laboratory at the California Institute of Technology. The highest resolution data - used here - was released in late 2015. Here's what the SRTM user guide says about the data:

  • "datasets result from a collaborative effort by the National Aeronautics and Space Administration (NASA) and the National Geospatial-Intelligence Agency (NGA – previously known as the National Imagery and Mapping Agency, or NIMA), as well as the participation of the German and Italian space agencies. Together, this international space collaboration generates a near-global digital elevation model (DEM) of the Earth using radar interferometry"

The data were collected from the Space Shuttle Endeavour over an 11 day period in 2000:

  • "SRTM was the primary, and virtually only, payload on the STS-99 mission of the Space Shuttle Endeavour, which launched February 11, 2000 and flew for 11 days. Following several hours for instrument deployment, activation, and checkout, systematic interferometric data were collected within a 222.4-hour period. The instrument operated almost flawlessly and imaged 99.96 percent (%) of the targeted landmass at least one time, 94.59% at least twice, and about 50% at least three or more times. The goal was to image each terrain segment at least twice from different angles (on ascending, or north-going, and descending, or south-going, orbit passes) to fill areas shadowed from the radar signal by terrain"

See this BBC article from 2000 about the SRTM mission - it's a very clear explanation. And here's a picture of the 60 metre long mast that was used to collect the data in the maps above. It's called the Able Deployable Articulated Mast (ADAM). There were radars on the mast and on the Space Shuttle itself.

This is where the SRTM data came from - more info here

* I don't even drink whisky, but I'll lose my Highlander card if anyone finds out so please keep it quiet