So, there I am, driving along in Edmonton, Alberta. I come to a stop light on Fort Road, look to my right and I see this:
Is that a building with longitudes written on the roof?!?!
And what are these longitudes? 9° 49’ W—that’s nowhere near Edmonton! Nor is 123°30’ E. What’s … going on here?
A little sleuthing via Google Maps later revealed that this was the Kathleen Andrews Transit Garage. It’s owned by the Edmonton Transit Service, which operates all of the buses and light rail in the city. But the rooftop details were part of an art installation by Thorsten Goldberg called 53° 30′ N. Each of the five structures on the roof (architecturally called lanterns) displays a longitude that directs us to a place on the earth at the same latitude as Edmonton: 53° 30′ N.
And—added bonus for shaded relief fans—that piece of terrain is then represented in 3D on the end of its lantern. Look carefully at the photo. There they are! They look for all the world like pieces of DEM rendered as Triangulated Irregular Networks in Blender.
For someone who spends a lot of time looking at terrain, this is the best kind of public art ever!
Before I go on, here are the five longitudes, in case you want to figure out for yourself where they are…
9° 49’ W
159° 08’ E
168° 10’ W
119° 26’ W
9° 49’ W
Mweelrea, County Mayo, Ireland
An unnamed gooseneck of the Amur River, which forms the border between China and Russia.
159° 08’ E
The 2958 m Kamchatka volcano volcano, Zhulanovsky (Жулановский), Russia.
168° 10’ W
Okmok Crater, Umnak Island, Aleutian Islands, Alaska
119° 26’ W
Mt Chown, Alberta
Here are some more images of the building from a CBC article.
“The collected mountain landscapes are Mount Chown at 119°25‘8.24“W in Alberta, named by the Methodist minister Samuel Dwight Chown; the crater with Mount Okmok, a volcano on Umnak Island, the Aleutian Islands in Alaska at 168° 6‘22.60“W; the Zhupanovsky Crater on the Kamchatka Peninsula at 159° 8‘25.04“E; an unnamed landscape near Dacaodianzi, Heilongjiang Sheng at 123°17‘54.95“E in China; and finally Mweelrea, the highest point in the province of Connacht at 9°49‘47.59“W in County Mayo on the west coast of Ireland.”
Kudos to the City of Edmonton and its Percent for Art policy, which stipulates that one percent of construction budgets goes to public art! This must be one of the most fun geography puzzles ever.
As we stepped out of the car, mosquitoes closed in. Having driven deep into the wilds of northern BC, I don’t know what else I should have expected. Fully seventeen hours north of Vancouver we had turned off a paved road onto an unnamed logging road with a shabby old sign for the “Derrick Creek Rec Site 6km,” one of the many gravel roads built for the giant logging trucks that prowl this far northern forest with their loads of valuable, recently chopped down, trees. Fallen trees that lay across the road had been sawed through by helpful earlier travellers. Only one was recent enough to block our path but we were able to lift it and pivot it off the road.
Mark slung a rucksack at me and and said, “Come on. This had better be good.” We donned wading boots and plunged into the forest.
The reason we were here was a cartographer’s dilemma. Derrick Creek, as I had first seen it on the Canadian topographic map poetically named “103P: Nass River” was a waterway that flowed south out of Derrick Lake and went some ten kilometres south to the Cranberry River.
The Cranberry, one of northern BC’s important inhabited rivers since time immemorial, and heart of the traditional lands of the Gitanyow First Nation, is shown on this same map winding back and forth, meandering its way westward, down to the mighty Nass, a river so provincially significant that in the coding of BC’s major watersheds it bears the halcyon number “500.”
103P “Nass River,” though, is a pretty small scale map, which means that while it covers a lot of territory it is not in any sense “zoomed in,” as we might say nowadays when we can pick up a phone and use our fingers like little stretching tools to zoom in on Google maps. 103 P, produced in 1989, is at the relatively undetailed 1:250,000 scale.
When you look at the more detailed 1:50,000 scale map 103P-10 “Cranberry River” (Second Edition, 1984, the most recent you can get), Derrick Creek, which the Gitanyow people call Xsimihletxwt (“green creek”), is visible in more detail. It flows out of Derrick Lake, passes around the letters WM, skirts a small swamp and goes into a small unnamed lake (near “23”), then flows south, crosses under the highway and into Bonus Lake. This is how Derrick Creek proceeds to the Cranberry. Quiet, reliable, placid. Probably infested with beaver.
(Bear that small unnamed lake near the “23” in mind. We’ll call it Unnamed Lake 1. It will become important later on.)
So, all good. Except, apparently no longer true.
Today, if you look at a online map produced by Natural Resources Canada, or Open Street Map, what you will see is that after leaving Derrick Lake, the creek goes south for a bit, then just before hitting that unnamed lake it appears to change its mind, and it heads west. It heads west, passes under the highway, through a second and bigger unnamed lake and goes into the Nass. No Cranberry River. No Bonus Lake.
This could be fairly significant if you told your friend “Lets go fishing at the mouth of Derrick Creek,” and she showed up at the place on the Cranberry, the place where a streams still flows in but apparently we don’t call it Derrick Creek any more, and you showed up on the Nass at that new Derrick Creek, like a second location of your favourite restaurant, recently built and all glitzy, but somehow lacking the charm of the original, and somehow too even the food doesn’t taste as good. Especially the fish.
In short, Mark and I are here to figure out what happened. Was it an old mapping error? Did Derrick Creek never flow to the Cranberry? Or did the stream change course, some time between 1989 and 2018?
You’ll also notice on the map above a swamp at the point where Derrick Creek allegedly changed course, and this may be helpful. Strange things happen in swamps. Water flows slowly and in multiple directions. Beavers do stuff, small actions of chewing down trees and pushing them into certain places in the creek flow, small acts that add up to big changes in the end. We’re here to look for evidence.
The old logging road that Mark and I now set off on, on foot, is overgrown with alder. Two old tracks of vehicle tires are still visible on the ground, and the dog weaves ahead easily along them, while at the height of my face alders slap me repeatedly. Which is welcome, because it’s brushing off the mosquitoes. It’s clear that no one had driven this road for about ten years.
After a few minutes of breathless alder crashing we come to an old log landing, a clearing in the forest where cut trees were stockpiled before loading onto trucks. There’s an old camp here with a small stove cunningly made from a steel barrel. We strike off at a bearing of 290° through a forest of evenly spaced pines, trees apparently planted some 40 years before. A few minutes later we hit the old channel of Derrick Creek, just above Unnamed Lake 1. It is neither stagnant nor non-existent. It is a small, burbling little stream. It is small, less than a metre across, and flowing with no great volume, but it does exist.
Why does this even matter?
Well, should the map looks like this (the old way)…
or like this (the old way)?
It’s a big difference.
But, it should be easy to decide. Here are the sites we need to visit.
Culvert 1, to observe what’s coming down the “old” Derrick Creek and flowing into Bonus Lake
Bridge 1, should be the same as what we see at Culvert 1
Bridge 2, to observe the contribution of an unnamed tributary that heads straight to Unnamed Lake 1
Bridge 3, to observe the outflow from Derrick Lake
The Split, to see what happens there
Culvert 2, to observe the flow in the “new” Derrick Creek, which, incidentally, is classified as “intermittent” in the provincial Freshwater Stream Network data
In the nineteenth century the standard way European explorers in Africa or Afghanistan decided which was the primary tributary of a river was to measure the flows of each at the confluence. This was height of the patriarchy, I know, but their simple science had a reasonable method: the stream contributing the greater amount of water got the name of the river, and up it the intrepid explorer went on the continuing quest for the headwaters. Admittedly this usually resulted in boundaries being drawn by Great Powers, and odd nation states being created for the purposes of the same said Great Powers, but we’re not doing any of that here. We know this is Gitanyow territory. We just need to figure out where Derrick Creek. really goes. It’s a cartographer’s dilemma and a cartographer’s errand.
And our problem is a bit different from that of the nineteenth century explorer. We already know where the headwaters are. Derrick Creek comes down from Derrick Lake. We’re trying to figure out where the resulting flow goes. But we can still use the principle that where more water flows, that’s the main stream. We’re just doing it … downhill.
Working our way upstream we come to the key place: on the edge of a large swampy clearing, Derrick Creek is flowing in from the east and splitting in front of me into one fork that continues west across the swamp and, presumably, eventually to the Nass, and one fork that lazily turns south and feeds this small stream that goes to unnamed lake #1.
Mind you this is not swiftly flowing water. Everything is at the same level, no doubt due to beaver dams. So the place the creek divides is more of a pond with two outflows. There’s no current to observe.
Mosquitoes close in as I survey the water and balance precariously atop hummocks of grass with water between them. We’re going to call this place The Split.
Down in the direction of Unnamed Lake 1, I can hear the water spilling over what is probably a beaver dam and beginning its descent. Looking at the surrounding forest I can see that there is a significant historical channel this way. To the west the swamp continues on as a wide opening in the surrounding forest and its unclear how the stream leaves it. At any rate it seems not a lot of water is flowing through here, at least not on the surface. Subsurface flow is possible.
I’m not able to measure how much water is leaving via the two exits at The Split. However, I have a bit of a proxy. If we go look at Culverts 1 and 2, we should be able to compare the flow through them and decide which is the bigger stream. These two points underneath the highway represent the only candidates for how water in Derrick Lake can leave the area, so they should tell us where the major stream is.
On the way out however it seems worthwhile to check the flows at Bridges 1, 2 and 3. And this introduces more uncertainty. At Bridge 1 we have a good flow of a creek a few meters across and fairly shallow, say 15 cm or less. At Bridge 2 we have the same thing, suggesting that most of what’s flowing down to Bonus Lake in fact comes from this unnamed tributary, and not from Derrick Lake at all. At Bridge 3 is the actual outflow from Derrick Lake and our first look at what is undisputedly Derrick Creek. The water here is sluggish. It might be a metre deep in the middle but there’s little flow. As if Derrick Lake isn’t really draining much at all.
So it’s on down to Culvert #1, where the “old” Derrick Creek flowed under Highway 37 and into Bonus Lake. Mosquitoes declare themselves in force, and drive us into amusing looking but useful white bug jackets.
Culvert #1 is impressive. It has been engineered for major flow, and is in fact enormous twin culverts, each about 4 metres in diameter. (They are such a major work of engineering as to have a highway sign, which identifies then as “Derrick Creek North Culvert” and “Derrick Creek South Culvert.” This suggests the BC Ministry of Highways has not been informed by the BC Ministry of the Environment about the new direction the creek took.) You could drive a small car through either of them. The flow of the creek, although decent, barely fills the bottom of these huge structures.
So now we visit Culvert #2, the culvert where the “new” Derrick Creek passes under highway 37. This is a shocker. We can barely even locate it because of the tiny size of the drainage and the almost inaudible water flow. The GPS is called in to confirm we are in the right place.
There’s almost no water here. And culvert #2 itself is small, less than a metre in diameter. No more than a trickle of water flows through it.
It’s plainly impossible that Culvert #2 carries is the main flow of Derrick Creek. The flow from The Split toward unnamed lake #1 may be lazy, but it’s more than we see here. Culvert #1 is carrying much more water, a real stream.
It looks like something is badly awry with the Freshwater Stream data for Derrick Creek, and I’m going to go with the old scheme shown on the maps from the 1980s: Derrick Creek flows out to the Cranberry.
But there’s a third possibility. What we saw at bridges 1, 2 and 3 suggests that most of what used to be, at Bonus Lake, called Derrick Creek comes from that unnamed tributary, and there’s actually very little water flowing out of Derrick Lake. It’s easy to imagine that before the current generation of beaver dams the outflow of Derrick Lake was sufficiently connected to this active stream as to give it its name, but that even then most of the water came from the unnamed tributary. There may need to be another reconnaissance one day. I can see it now: a canoe, little stream gauges, perhaps a drone….
Back in the car, Mark seizes the packet of topographic maps we’ve been using for reference and says, “I know how this thing can be really useful.” He begins swatting bugs with it.
there are only two sun azimuths to select from: 315° (northwest) and 225° (southwest). More flexibility would be good, because each landscape seems to have a different ideal azimuth to bring out the landforms that you want to bring out. More about this down below.
there’s no height exaggeration possible
occasionally there are odd artifacts, like straight lines running across the hillshade
On the other hand, you can adjust its brightness and contrast, and use the Multiply blend mode, which means you can do some nice things with it.
But, if you want to adjust the azimuth or exaggerate height, you’ll need to find a DEM and make your own hillshade. It’s well-established (though not well-explained) that the human eye needs to see light from above, preferably from above and to the left. If your map is, say, south-up, you will need a hillshade where the light comes from the southeast (which will be in the upper left).
The overall process
Let’s talk about the three principles.
The hillshading algorithm requires a DEM in a metric projection. That means that DEMs projected in degrees won’t work: you have to re-project them first. [Although maybe sometimes not.] Unfortunately, just about all DEMs come projected in degrees, so re-projection is a must. (The Geospatial data extraction site at canada.ca, however, is one that does offer DEMs projected in metres. Choose to download your data in the “Canada Atlas Lambert (EPSG: 3979)” projection.)
The scale of your final map determines what sort of cell size you want in your re-projected DEM. A DEM with 10m cells is far too detailed for a map at 1:500,000, and the file would be enormous. On the other hand, a cell size of 500m would make a very coarse hillshade at 1:500,000. As a general guideline, divide the denominator of your scale by 3,000 (for screen display) or 10,000 (for printing at 300dpi) to get roughly what cell size you want. So if your map is 1:100,000, and it will be printed at 300dpi, you’d be looking for a DEM with (roughly) 10m cells.
In QGIS it is an option to style any DEM as “Hillshade” (other options are singleband grey, multiband colour, paletted, singleband pseudocolour, etc.) but the GDAL hillshading algorithm in the toolbox (Processing>Toolbox) produces a better result.
Acquiring DEM data
The first thing you need to do is pick your resolution. Because DEMs usually come projected in 4326, DEM resolution is typically expressed in arc-seconds, or seconds of latitude. Because degrees of latitude in Canada are bigger than degrees of longitude, these cells are not square on the ground. They are rectangles that are taller (north–south) than they are wide (east–west).
What you want to know is how these non-square cells measured in arc-seconds will convert to square cells measured in metres. Here are some rough ideas.
From here, I’ll demonstrate how this works with an actual example. In this case I want shaded relief for a series of maps that are all in the same area, and range in scale from 1:45,000 to 1:130,000. Looking at the chart above, this scale range suggests I can get away with using SRTM1.
Once they are downloaded and unzipped, I’ll read them into QGIS to confirm that they cover the right area.
Merge and Clip
You will want to merge all of the individual DEMs into one, using Raster>Miscellaneous>Merge. (Incidentally, they do not have to be read into QGIS to do this.) If you made shaded relief out of each individually, there would be some artifacts along the lines where tiles meet.
I tend to name the resulting merged DEM with “_4326” on the end so that later I will know what projection it’s in.
It’s tempting to display as hillshade now, but don’t. The hillshade styling is not meant for DEMs projected in degrees.
If you want to clip the merged DEM, now is the time to do it. Remember that with Raster>Extraction>Clipper you will need to change the QGIS projection to the DEM’s native projection (4326) before you draw the clipping box. Be sure to check, once you come back to your map’s projection, that the clip you made covers your whole print composer.
Re-project and re-sample
Reprojection is the process of giving raster cells coordinates in a new projection. Resampling, on the other hand, is the process of changing the resolution of the DEM. The two are essentially inseparable, since as you reproject from 4326 to, say, 32609, you will also want to go from the rectangular cells of the degree-projected DEM to nice square cells in the UTM projection.
The first thing to do is to right-click the DEM and choose Save As… so you can see the dimensions of the original DEM cells.
Note that once you set the CRS for the saved copy to be 32609, you get a suggested resolution of (roughly) 17 x 31m cells. That’s the native cell size of this SRTM DEM at this latitude. Note down the “17” (the smaller dimension) somewhere, and close this dialogue.
You can reproject and resample using QGIS’s Save As… feature, but you don’t get control over the resampling algorithm used, and the results, once you get to the final hillshade, are ugly.
Instead, you want to re-project and re-sample with the Warp tool in the toolbox. (Go Processing>Toolbox and search on “warp.”)
In this dialogue…
Source SRS should be 4326
Destination SRS should be 32609 (or whatever metric projection you are making your final map in)
Output file resolution can be whatever you want, but I get good results with the smaller of the two cell dimensions I saw in the Save As dialogue — in this case, 17.
Trial and error with making hillshades has convinced me that the best resampling method to choose here is “bilinear.”
I name the resulting DEM with a “_32609” on the end so I will know its projection in the future.
The new 32609 DEM should look the same as the 4326 DEM when read into QGIS, but if you go to the Metadata tab in Layer Properties you’ll see it has a cell size of 17 metres, and quite different pixel dimensions.
For your final hillshade, the one you use in your map, you will want something better that what you get if you just style this DEM as “hillshade.” But for now, go ahead and style it as “hillshade.” This enables you to play with the sun azimuth and elevation, and the vertical exaggeration, to see what is going to work best for your terrain. The human eye probably wants an azimuth around north-northwest (337.5) but there are a lot of azimuths on either side that will work.
Notice how changing azimuth changes what’s brought out in this piece of terrain:
Make a static hillshade
Now if this DEM-displayed-as-hillshade has no strange artifacts, you’re done. But if you want a smoother results, it’s time to take the azimuth, sun elevation and vertical exaggeration you’ve chosen, and go over to the GDAL Hillshade tool in the toolbox. (Go Processing>Toolbox and search on “hillshade.” Notice that two different hillshade tools are available: a QGIS one, and a GDAL one. The GDAL one has an interface I prefer.)
Enter your vertical exaggeration under Z factor, your sun azimuth under Azimuth of the light, and sun elevation under Altitude of the light. Generally speaking you leave scale as 1.0000, because your have re-projected your DEM and the vertical units and the horizontal units are both metres.
And here’s the result
Hillshaded made by GDAL tend to be a bit darker than we want. Their raster values run from 1 to 255, and by default this gets displayed as a singleband greyscale from pure black to pure white. But you probably don’t want pure black areas in your map, or at least not very many. Areas of solid black can’t have much information in them.
Two common solutions are to adjust the opacity of your hillshade, or to increase its brightness.
A solution that I like is to build a colour ramp that runs from 50% grey (#808080) to white (#ffffff),
and then display the hillshade as singleband pseudocolour, using this colour ramp.
What I like about this is that I then know that no part of my hillshade is darker than 50% grey.
Typically you combine the hillshade with the other layers of your map by assigning it a Blending mode of Multiply.
So you can get something like this.
Be aware that if you have other layers in your stack that have partial opacity, it does make a difference whether your hillshade is above or below them. In general you get the most predictable results by using a Blending mode of Multiply and placing the hillshade at the top of your stack.
That’s it. Using these techniques, you should be able to manufacture hillshades with any azimuth, pretty much all over the world. It gets the most challenging when you are mapping at large scales like 1:20,000.
OpenStreetMap data is often the best large-scale data you can find in regions of the world where governments are not yet distributing free, open geodata.
There are several ways to download OSM data (QGIS plugin, Geofabrik, direct from OSM), but if the format you prefer is shapefile, and you have a specific area you’re interested in, the old Weogeo service may be the easiest and the best way.
Weogeo seems to have been bought or otherwise taken over by the for-profit company Trimble. I appreciate Trimble hosting this service and keeping it alive, but since Trimble integrated it into their pre-existing sales system, you have to go through a number of odd steps to get your free data. Since it’s free, open data, you hope for one of those good-feeling interactions that suggest the sharing-without-strings that OSM represents. Instead be prepared here for a less comfortable, more corporate, interaction where they’ll want to you to go to their “data marketplace,” make an account, “add to cart,” and so on. But it works really well.
Two important notes up front:
If you use the Firefox plug-in “Privacy Badger,” it breaks this site. You have to disable it for trimbledata.com.
You won’t get your data immediately. Depending on the order size you may have to wait up to 24 hours to receive the email saying that you can download it.
Click Shop OpenStreetMap data now. You are now at the Trimble Data Marketplace.
Sign In (upper right corner). (Registration is free, and necessary.) Your name should now appear in the upper right hand corner, and below it, over the northwest portion of the map, you should see a summary of your current order, with headings for Region, Layers, Datum-Projection and File Format.
Initially the map shows the entire world (in a ghastly pseudo-mercator projection, but that does go hand-in-hand with OSM). Region is “Entire map,” Layers are “26/26” (26 of 26 available layers), Datum-Projection is “Lat/Long-WGS84 (Native),” File Format is “ESRI Shape,” Estimated size is “1.36 TB” and cost is “Free.
Don’t be fooled by the 1.36 TB. That’s the size of the entire world database for OSM. Trimble will restrict you to a 5 GB limit in a single order.
On the map you can now pan and zoom to the region you’re interested in. Let’s say you go to the area around Budapest, Hungary.
Notice that even though you are zoomed in, the Region is still “Entire Map” (meaning the whole world) and Estimated Size is still 1.36 TB. To narrow down your data area you have to either upload a KML file with a polygon of your area of interest, or draw a polygon on the screen.
To draw a polygon, click the pencil icon next to Region, click Draw, and begin placing points around your polygon. Clicking on the initial point closes the polygon. Now Region and Estimated Size change to something more reasonable.
You may not want all 26 layers, and you can click the pencil icon next to Layers to select the subset you want. The 26 layers are explained in depth at the OSM wiki page on Map Features, but for simplicity I’ll just list the 26 categories here, with links to the OSM wiki page:
Note that these categories are often subdivided into separate shapefiles for point, line and polygon features.
In this case let’s say I want only Waterway, Highway, Railway. I deselect all, select these three, and click the “X” to close the Layers list. Layers has now changed to “3/26” and Estimated Size has now dropped to 381 MB.
Then click Order. Accept the Content License and click Add To Cart. Click View Cart.
Everything should still read “Free,” so click Checkout. Go through the [annoying] Address Information and Select Payment steps (“No Payment Required”) and then finally Place Order.
The next step is that you receive a series of emails acknowledging your order, telling you that your order is being prepared, and finally that your order is ready for download. It can be almost immediate for small orders, or up to 24 hours for large ones.
When you do download your data it will be in a ZIP file called “weogeo_<order number>.zip.”