Derrick Creek: A Cartographer’s Dilemma

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 blocke 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.

103P detail 2

103 P “Nass River,” 1989 1:250,000

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.

02_103P10 detail

103 P 10, “Cranberry River,” 1984, 1:50,000

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 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.

06_CBMT annotated

03a_CBMT

Detail of the area where Derrick Creek has apparently changed course

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)…

05_basemap v2

or like this (the old way)?

04_basemap v1

It’s a big difference.

But, it should be easy to decide. Here are the sites we need to visit.

00 map of sites

Roads, streams and lake from current provincial data; “indefinite” streams shown in lighter blue. Contours from SRTM 1″ coverage.

  • 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.

Derrick Creek fork

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.

DSCF3975

Culvert #1

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.

Derrick Creek (Nass) culvert Hwy 37

Culvert #2

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.

 

 

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Maps for Θεσσαλονικη/Thessaloniki

On a recent trip to Thessaloniki I acquired quite a few maps of the city. It turns out that finding a really good one is not trivial. Here’s the one I kept going back to:

Fraport map

This is the Fraport map which is available for free at the airport. (I found a display of them in the baggage claim area.) I’ve written in the bus routes on the major avenues myself. The cover looks like this:

Fraport map cover

But I was not able to get a hold of this map before arriving. The map that I printed out at home was this one:

DSCF2678

You can download this as a PDF from https://visitthessalonikigreece.com/about-thessaloniki/thessaloniki-maps/   It’s good but a bit hard to read.

Some of the other maps you can acquire in Thessaloniki itself are worth looking at. The next three I picked up at the tourist information point at the bottom of Aristolelous. Here is their Thessaloniki City Map:

city map

As you can see, not all streets are labelled. Its cover looks like this:

city map cover

 

And there is the even more spare Thessaloniki Museums’ Map:

museums map

and its cover…

museums map cover

And the Thessaloniki Monuments Map:

monuments map

with its cover (this is the Greek edition):

monuments map cover

I have to say the Museums’ and Monuments Maps are so skeletal as to be useless for navigation in the city. Also, there’s some inconsistency.  The Museums’ map and the Monuments map both identify the street that leads south from Antigonidon Square to Egnatia as “Παπαζωλη/Papazoli,” whereas the other maps agree that it is called “Antigonidon.”

A map that I bought in a bookstore was this “Best of” map:

best of map

Its cover:

best of map cover

It’s pretty good, but the lamination actually caused me not to use it. Too hard to draw on.

Last but not least, that all-important bus route map. You can get this at the tourist info point as well.

bus map

Its cover:

bus map cover

This is a tiny map, and not quite as detailed as you might like, but oh-so-valuable. You don’t use it for finding your way around on foot, only for figuring out where bus routes go and which one you want.

A Little Geometric Creativity

There’s a nice old geometric pattern…

figure00

…that Eric Broug presents in his book Islamic Geometric Patterns as being from the Great Mosque of Herat.

Its construction is based on a hexagon, and the pattern repeats as additional hexagons are tiled around the first one. The underlying hexagons (which are not drawn in the finished pattern) are shown in red here:

figure00a

This makes a fine star/wedge/triangle pattern that is quite satisfying to look at, and suitable for decorating things in your house.

The construction of one of the hexagon-based units of the pattern begins with drawing a circle, and then a hexagon within that circle. Once the hexagon is drawn, the lines of the pattern can be drawn within in it.

But in the real world, a medium on which we are drawing (or painting) always has edges, and those edges do not go along the edges of the hexagons. For example, let’s say we want to draw one of the pattern units, plus however much extra fits, on a square board or tile. Something like this:

figure00b

Draw in the supporting hexagons and you will see that the one complete pattern is indeed surrounded by only parts of adjacent copies of the pattern.

figure00c

It’s a bit of a construction conundrum. How will we fill in the portion of the pattern that lies outside the one central hexagon that we will have room to draw? How will we extend the pattern to the edges of the square when we cannot place a compass foot at the centre of any of the adjacent circles that would define the basic hexagons?

There is a way.

Let’s review how the pattern is made, and then examine how to extend it without being able to draw more circles. Follow along with your own piece of paper, pencil, compass and straightedge.

There is something magical in the fact that this pattern, with all of its exact proportions, can be constructed solely with a compass and a straightedge. You never need to measure an angle or a line.

To construct a hexagon, one begins by drawing a circle.

figure01

Within the circle inscribe a hexagon using the standard method of walking the legs of your compass (still set to the same radius) around the circle. We’ll call this Hexagon A. It is oriented so it is a point-up hexagon.

figure02

Draw radii through all the vertices of the hexagon. We’ll call these the ribs of hexagon A.

figure03

 

Now we need to construct a second hexagon of the same size, and on the same centre, but rotated 30°. To do this we will connect the midpoints of the six arcs from the hexagon already made.

If we had plenty of room, we would find those midpoints by first drawing six more circles (of the same radius) centred on the six vertices of hexagon A; and then draw lines from the centre of the original circle to the outer points of intersection of adjacent secondary circles. These ribs (purple, below) would show us the midpoints of the arcs.

 

figure22But with the limited space we are working with, we need instead to bisect one side of the hexagon. This can be done with two compass arcs from adjacent vertices of hexagon A; we can then connect their intersection outside the circle with the circle’s centre.

figure04

This line bisects one of the arcs, and we can use that as a starting point for making a second hexagon. We’ll call this Hexagon B, and it is oriented so it is a side-up hexagon.

Draw ribs for hexagon B.

figure05

Note that the ribs of hexagon B (purple) go through the midpoints of the sides of hexagon A (red).

Connect the hexagon A midpoints to make a six-pointed star. We’ll call these star 1 lines (green in the next figure).

figure06

Similarly, we can note that the ribs of hexagon A pass through the midpoints of the sides of hexagon B. Connect the midpoints of hexagon B to make Star 2 — being sure, however, in this case to extend the star lines beyond hexagon B as far as the first edge of hexagon A you encounter. We’ll call these star 2 lines (blue in the next figure).

figure07

Finally, we ink certain portions of the Star 1 and Star 2 lines to make the final pattern. Note that the entire pattern lies within hexagon A.

figure08

The pattern that is inked consists only of portions of star 1 and star 2 lines. In fact we drew hexagons A and B, and their ribs, only to create the star 1 and 2 lines. And we drew the initial circle only to create hexagons A and B.

In order to extend the pattern we need to draw more star 1 and 2 lines outside our original hexagon. On a larger medium we could easily place the centres of new circles outside hexagon A, but on this limited surface where we are working we cannot.

It may help to look at what we need to find.

figure21

From our earlier construction of adjacent hexagonal cells, we know a few things about what should be happening. Star 1 lines leaving the hexagon (A in the diagram above) go a certain distance to a point Y (which we’re not really sure how to locate) and then turn through 120° to follow a line D.

Star 2 lines leaving the hexagon (B in the diagram above) go a certain distance to a point X (which we’re not really sure how to locate) where they cross a star 2 line (C) in the adjacent hexagons. At some farther point Z they also go through 120° turns.

As well, it’s valuable to make a few observations about what happens as these lines enter adjacent hexagons…

1. Hexagon A sides, when extended, become the ribs of other hexagons A, and vice versa.

figure10

2. Star 1 lines become some of the star 1 lines of adjacent hexagons.

figure13

3. Star 2 lines become some of the star 2 lines of adjacent hexagons.

figure14

This means that by extending these hexagon sides, ribs and star lines, we have much (but not all) of the construction information for the pattern outside the original hexagon.

figure16

What’s missing are lines C and D, and points X, Y and Z.

But now we can see that point X is the place where the extended hexagon A sides meet the extended star 2 lines. Drawing a line through them gives us line C.

figure17

Similarly, Point Y is the place where the extended hexagon A sides meet the extended star 1 lines. Drawing a line through pairs of points Y gives us line D.

figure18

At this point we have all the construction lines we need to ink the rest of the pattern outside the original hexagon…

figure19

…and then remove the construction lines.

figure00b

It’s very satisfying to be able to construct this figure in a limited space, and to solve the problems associated. But now, as a bonus, it appear that the pattern presents us with a fascinating geometry problem!

As the pattern is extended, a new, larger hexagon has appeared, a hexagon that is similar to hexagon B, but is formed by star 1 lines that pass on the outside of the six small triangles. We’ll call it hexagon C. In the illustration below, hexagon B is purple, and hexagon C is blue.

figure23

It’s a bit of a puzzler, but I’ll just leave the problem here for the intrigued reader to solve. In terms of the side length of hexagon B, what is the side length of hexagon C?

Making shaded relief from digital elevation models (DEMs) in QGIS: a British Columbia perspective

Who would not agree with Tom Patterson, creator of the fabulous shadedrelief.com website, when he said, “There is no more important component of a map than the shaded relief.”

But the topic of creating your own shaded relief from a DEM is rather complex, so I’ve made a few assumptions in this how-to. I’m assuming:

  • you know your way around QGIS (I am using QGIS 2.18 for this post)
  • you’re familiar with the idea of projections, and re-projecting raster data
  • you know that each projection/datum combination has an EPSG number, which is a convenient way to refer to it. For example
    • Lat/Long/WGS84 = 4326
    • UTM Zone 9N/WGS84 = 32609
    • BC Albers = 3005

If that’s the case, there are really only three things you need to know in order to made your own hillshades:  where to get the data, how to transform it, and what pitfalls to avoid.

Why even make your own hillshade?

Usually when I want to include shaded relief in a map that is in British Columbia, the first place I will turn is the WMS service at openmaps.gov.bc.ca: http://openmaps.gov.bc.ca/imagex/ecw_wms.dll?

001_WMS hillshade example

The 315 black-and-white hillshade from openmaps.gov.bc.ca. The black-and-white hillshade with the sun at an azimuth of 315° is typically the most useful of the layers on this WMS server.

It’s got some limitations:

  • 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.

002_WMS hillshade example with overlay

When you set the blend mode of a hillshade to MULTIPLY, it shows through upper layers.

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).

004_WMS hillshade example rotated 180

Now south is at the top (map is rotated 180°) and the shaded relief appears flat or inverted. For this map you would need a hillshade where the sun’s azimuth is southeast, or 135°.

005_DEM hillshade rotated 180

Here the map is still rotated 180°, but the hillshade has been manufactured with an azimuth of 135°. The mountains look like mountains again.

006_DEM hillshade rotated 180 3x

A 3x vertical exaggeration of the terrain emphasizes the detail in the valley bottoms.

The overall process

007a_flow chart

Let’s talk about the three principles.

  1. The hillshading algorithms require a DEM in a metric projection. That means that DEMs projected in degrees won’t work: you have to re-project them first. Unfortunately, just about all DEMS come projected in degrees.
  2. 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 5000 to get roughly what cell size you want. So if your map is 1:100,000, you’d be looking for a DEM with (roughly) 20m cells.
  3. It is an option to style any DEM as “Hillshade” (other options are singleband grey, multiband colour, paletted, etc.) but the 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 BC are bigger than degrees of longitude, these cells are not square. They are upright rectangles.

What you want to know is how these non-square cells measured in arc-seconds will convert to square cells measured in metres. Here’s a handy chart.

resolution degrees resolution metres pixel size in degrees source limitations recommended scale Notes
1/3 “ 6 9.26E-05 ftp://rockyftp.cr.usgs.gov/vdelivery/Datasets/Staged/Elevation/13/ArcGrid/ USA only ~ 1:30,000 It comes as 1°x 1° tiles. Files have names like “USGS_NED_13_n19w068_ArcGrid.zip,” which would be the 1°x 1° tile northeast of 44°N, 110°W.
1” 17 0.000208333 SRTM 1 for all of North America at http://rmw.recordist.com/
Europe at https://www.eea.europa.eu/data-and-maps/data/eu-demre
North America and Europe ~ 1:100,000 From recordlist these come as 1°x1° tiles in HGT format, each about 25MB. The file N55W128.hgt would be north and east of 55°N, 128°W
3” 45 0.000833333 This coverage, based on SRTM data, is available for the world in two different versions.

worldwide~ 1:300,000v4 data is better, but it comes as 5°x5° tiles. The SRTM 3 comes as 1°x1°tiles in HGT format. The old CDED dems were this resolution.

15”4500.00416667http://www.viewfinderpanoramas.org/dem3.htmlworldwide~ 1:1,500,000  250m and 500m https://hc.box.net/shared/1yidaheouv (Password: ThanksCSI!) worldwide~ 1:1,000,000 and 1:2,000,000re-samplings of the finer resolution data30”1 km0.00833333https://lta.cr.usgs.gov/GTOPO30 Or https://earthexplorer.usgs.gov/worldwide~ 1:3,000,000at this point you should be considering the shaded relief at http://www.naturalearthdata.com/5’10 km https://www.eea.europa.eu/data-and-maps/data/world-digital-elevation-model-etopo5worldwide~ 1:30,000,000 

You’ll notice that I favour the DEMs created from the Shuttle Radar Topography Mission (SRTM). These have a few advantages over the DEMs produced by Natural Resources Canada or the provincial mapping agencies:

  • they are usually more recent (dating to about 2000)
  • they represent actual measurements, as opposed to a grid generated from contour lines
  • they go right across provincial and international boundaries

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 I’m making. All the maps are in the same area, and they range in scale from 1:45,000 to 1:130,000. Looking at the handy chart above, this scale suggests I’m going to want to use SRTM 1 DEM.

007c determining the tiles you want2

Displaying an area in a print composer with grid of lines in CRS 4326 is one way to figure out which tiles you’ll need.

So I go to Recordlist, enter the bounding box and select SRTM1.

008_recordlist selecting DEMs

Downloading DEM tiles from Recordlist

Once they are downloaded and unzipped, I’ll read them into QGIS to confirm that they cover the right area.

Merge and Clip

You 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.)

016_merging DEMs

QGIS’s raster merge dialogue

I tend to name the resulting 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.

040_displaying as hillshade when projected in degrees

Styling the DEM as “hillshade” produces ugly results when the DEM is 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 creating new cells based on old cells at a coarser or finer resolution. 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.

050_Save As dialogue

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.

060_hillshade produced with QGIS Save As

When you reproject using Save As…, the final hillshade sometimes has these weird cross-hatching artifacts in it

Instead, you want to re-project and re-sample with the Warp tool in the toolbox. (Go Processing>Toolbox and search on “warp.”)

084_reprojecting using gdalwarp through QGIS toolbox

The toolbox’s Warp tool

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 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 Hillshade tool in the toolbox (go Processing>Toolbox and search on “hillshade”). This will produce a raster hillshade that you just display as singleband grey. It also tend to be about half the file size of the DEM itself.

086 running toolbox hillshade2

The toolbox’s Hillshade tool

And here’s the result

090_hillshade produced with gdalwarp gdaldem hillshade

Look, no artifacts!

Displaying hillshades

Typically you put the hillshade as the bottom layer in your map, and adjust brightness and contrast — because hillshades tend to be a bit darker than you want. Usually it’s brightness up, contrast down. Sometimes you will also make it semi-transparent.

More important, in terms of getting the rest of you map layers to appear to drape over your hillshade, is to set the blend mode of the hillshade to Multiply.

091_adjusting brightness etc

Multiply causes the values (lightness, darkness) in the hillshade to be adopted by layers above it.

So you can get something like this.

095_final result with multiply

Overlaying a hillshade whose blend mode is set to Multiply

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.

Finally, if you master this, and you are really in love with shaded relief, you will want to experiment with making shaded relief in Blender.

Tracing the Great Southern and Western

The “Ring of Kerry” is a 180 km tourist route around one of the rugged peninsulas on the west coast of Ireland. Although its moniker probably arose in a 20th century tourism promotion, the  route itself is one that travellers in the neighbourhood of the Irish town of Killarney have been encouraged to go round since the 1800s.

Here is Samuel Carter Hall, in his 1858 traveller’s guide, A Week At Killarney, expanding in full Victorian eloquence on why one might make this journey:

We shall ask the reader to accompany us to the wild sea-coast of the South-west, and the Tourist to follow us into a district where the graceful beauties of Killarney may be contrasted with the wild grandeur of scenery certainly unsurpassed in Ireland. That district is now visited by a large number of those who visit Killarney; and one of our special objects in our latest tour–in 1858– was to describe the routes to it, with the facilities for travelling and accommodation; and at the same time to picture its peculiarities as well as our limited space and opportunities permit us to do.

The district Hall is referring to is the Iveragh peninsula, jutting west into the Atlantic from the area around Killarney. Hall’s tourist is to begin from Killarney and proceed south to the town of Kenmare — which anchors the southeast corner of the peninsula; then out along its southern coast, up around the end, and back along the north coast to Killarney. With horse and jaunting cart the tour took the Victorian traveller two days. (Hall recommended hiring a single set of horses for the entire journey.) Today most visitors drive it in one.

But not all visitors have explored the Iveragh peninsula by horse-drawn car or horseless carriage.  Some 35 years after Hall published his guide, a new option appeared: rail. The West Kerry Branch of the Great Southern and Western Railway began its service in 1893, running along the north coast of the Iveragh from Farranfore to Reenard Point. Farranfore was a connection with the main line running from Tralee to Killarney and on to Cork; Reenard Point was a ferry terminal on the outermost coast where passengers could board a boat and continue out to Valentia Island, a place sometimes promoted with the tantalizing (but geographically incorrect) fact of being the westernmost point in Europe. However it is fair to say that the GS&W was the westernmost railway in Europe.

1902 route map

The West Kerry Branch of the GS&W highlighted in yellow. (Map from Project Gutenberg: “Great_Southern_and_Western_Railway_-_1902_Ireland_routemap_-_Project_Gutenberg_eText_19329.jpg”)

Tourism was only one reason for this thirty-mile rail line out to the end of the world. Valentia Island hosted both famous slate quarries and an active fishing industry, and there was demand for the products of both in Ireland’s big neighbour to the east. No less a symbolic building than the Houses of Parliament in London was floored with Valentia slate.

This branch line ceased operations in 1960, and today most stations and track – which was the Irish Gauge, spaced 5′ 3” apart – have been removed. But, if you’re paying attention, you can still encounter bits and pieces of the railway, which visited the towns of Killorglin, Glenbeigh and Cahersiveen on its way.

 

DSCF0178

In Killorglin a plaque on the sidewalk, near the Aldi supermarket on Iveragh Road, tells the story of this vanished line.

For example, in the village of Glenbeigh, if you cross the River Behy on the old bridge and go just a short distance left, you find the road cutting through the old railgrade, still some ten feet high.  The Gleensk Viaduct looms above your head as the road does a tight turn to contour through a small drainage on the steep-sided hill.  At Cahersiveen the old rail bridge stands just upstream as you cross the river Ferta.

 

DSCF0042

On the way to Cahersiveen, the road snakes high above the Atlantic along the side of Drung Hill, and here a roadside pullout features an interpretive sign that details the history of the GS&W.

DSCF0043

At the same location: the mouths of two railway tunnels are above the road but below the electric line running across the slope

In many ways though the most remarkable remains of the railway are the mute raised railbeds that run through farmers’ fields.

 

DSCF0182

Do the cows know that a railway used to run along that strange, straight mound that cuts through their field? (Muingaphuca townland, near Killorglin)

As well, the railway is detectable in small kinks in present-day roads, like the one in the Caragh Lake Road 200m from where it meets the Ring of Kerry. Here the line crossed over the road, which jogs briefly to pass under a viaduct that is now completely gone.

There’s a remarkable web resource for tracing this old route. The Historic Environment Viewer of the Irish government’s Department of Arts, Heritage, Regional, Rural and Gaeltacht Affairs features a detailed basemap from Ordnance Survey Ireland (OSI) which shows the current status in superb detail at large scales.

 

Screenshot from 2017-08-23 15-54-25

OSI’s superbly detailed and up-to-date map of the area between the Caragh River (right) and the village of Glenbeigh (left). Portions of the old rail line are shown.

But here’s the magic: you can change the base map to the Cassini 6″ mapping. This is mapping at six inches to the mile (or 1:10,560) from the late nineteenth or early twentieth century, perfect for seeing where the railway ran. It turns out that, as one drives the Ring of Kerry from Glenbeigh to Cahersiveen, the old rail grade is never far away, sometimes running on the right, sometimes the left, side of the road.

 

Screenshot from 2017-08-23 10-39-19

The same region, but now seen against the Cassini 6″ basemap, c. 1900

As well, there are two other historic map layers here. The Historic 6″ dates from between 1829 and 1841; the Historic 25″ (twenty-five inches to the mile, or 1:2534!) from the end of the nineteenth century.

There was a hope at one time that trans-Atlantic vessels would depart from Valentia Island, passengers preferring to go as far towards North America as possible by rail before boarding ship. It never came to pass, but today the old rail line may perhaps have another life. Between Glenbeigh and Reenard Point the rail bed is presently the locus of debate about whether it will be turned into a cycleway. The conflict focuses on how local landowners will be compensated. If this can be worked out, yet a fourth mode of transport will be added to the choices travellers have had for exploring that peninsula west of Killarney.

 

 

Downloading OpenStreetMap data through Trimble

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:

  1. If you use the Firefox plug-in “Privacy Badger,” it breaks this site. You have to disable it for trimbledata.com.
  2. 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.

Here’s the procedure:

Go to http://market.weogeo.com/datasets/osm-openstreetmap-planet.html

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.Trimble1

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.Trimble2

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.Trimble3

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.”

Mapping Gottfried Merzbacher’s “The Central Tian-Shan Mountains 1902-1903”

In 1905 Gottfried Merzbacher, a geologist, published an account of two years exploring the Tian-Shan.  The Central Tian-Shan Mountains, 1902-1903 (John Murray, London) is an engaging read, partly because of Merzbacher’s insights about the landscape, and descriptions of the people he meets, but also because it is an account of his efforts to solve the puzzle of where the prominent mountain of Khan Tengri actually was. This 7000m peak was readily visible from lowlands outside the Tian-Shan, but previous mappers had merely been able to theorize about how one might get to its base.

Merzbacher’s book originally came with a map, but, as is so commonly the case, the map was not properly scanned for the digital copies of the book that one can download today from archive.org. You get a fragment like this:

merzbacher-map-fragment-2-colour

It’s a shame. Hopefully someone who owns the book will post a good scan of the complete map one day.

What fascinates me about these exploration accounts is the question How would we follow his route today? To that end I’ve begun mapping Merzbacher’s travels as described in The Central Tian-Shan Mountains. So far I’ve mapped Chapter 1.

merzbacher_chapter_01

(Download as PDF)

The key decision in this kind of mapping is what base map to use. Use a period base map (something from around 1900) and you may not be able to follow it today: place names change, roads move, and mountains get mapped more precisely. (See my previous post on the yet-moving location of Khan Tengri.) Use a modern map and you lose the sense of travel in an era of inaccurate mapping.

I tend more to the modern map. To me, the question Where did he go? means Where was his route relative to modern landmarks? But many modern base maps are unsuitable. Most online mapping services do not label rivers or mountain ranges. A modern road map (like Freytag+Berndt’s Central Asia) is too small-scale (1:1,750,000) to see what’s going on. So in this case I settled for a 1980s aeronautical chart (Tactical Pilotage Chart F-6C) which gives shaded relief at a reasonable scale (1:500,000) plus the added benefit of named rivers and mountain ranges. It ain’t that pretty though.

Representing Timberline

When I taught map reading in the U.S., there was a piece of folklore that we used to tell our students: that the green areas on the USGS topographic map indicated there was a sufficiently dense forest there that you could hide a platoon of soldiers (about 40 people) per acre. It was a good way to explain why small clumps of trees (or “tree islands”) didn’t appear on the map.

This story lives on on the Internet, but there’s no evidence that it’s really true. I like the implied subtext — cartographers producing the maps for military officers involved in some kind of domestic war, and needing to know where they could hide their men from aircraft –- but it doesn’t take much reflection to realize that the U.S. Geological Survey never could have visited all those places, looked at the tree cover, and decided where you could or couldn’t hide 40 guys. Or even how to divide it up into suitable one acre blocks.

In Canada, the green area on the topographic maps has a specific definition. According to Natural Resources Canada it’s “An area at least 35 per cent covered by perennial vegetation of a minimum height of 2 m.” And they probably estimate that 35% coverage from air photos.

NRCan topo_sm

So, when you’re ascending a mountain and the green ends on the map, is that treeline, or is it timberline? I’d always thought these were just variant terms for the same thing, but then I read Jim Pojar’s book Alpine Plants of British Columbia. In the Introduction to this photo-rich handbook of all the plants you’re likely to see up there, I learned that treeline and timberline are different:

The term treeline designates the upper limit of the occurrence of tree species, regardless of their stature, whereas timberline refers to the upper limit of forest, of continuous cover of upright trees 3 m or more in height.

So timberline, being where the solid forest ends, is the end of green on our classic NRCan topos. Treeline is the last little, twisted, stunted tree.

Neither, of course, is really a line. As map scale decreases and you zoom in, the timberline becomes impossibly complex, and has to be generalized somehow. And no map, I think it’s fair to say, tries to represent treeline, since this would somehow be defined by many isolated clumps of krummholtz (“twisted-wood”, the bonzai-like tree clumps also known affectionately as shintangle) that you see after ascending past timberline. And just to make things a bit more complicated, as the climate changes it has become easy (in northern BC at least) to find areas above treeline where dozens of tiny seedlings are coming up and now surviving. How big would they have to be before one moves treeline?

Timberline however is a very important landmark for hikers and skiers, and how to represent it is a question that comes up frequently in topographic mapping. Of course using using generalized green and white is not the only option. I first learned this when I was bushwhacking across a 1:50,000 scale “provisional” series, black-and-white topographic map in northern BC. On these there is actually a black line that snakes across the elevation contours. It has “W” on one side of it (for wooded) and “C” on the other (for clear). Little pairs of tick marks pointed into the forested side. It was hard enough to read that I took a pencil crayon and shaded in some green on the W side.

NRCan BW topo_sm

There’s also the solution that National Geographic used years ago in mapping northern Canada; the Northern Limit of Wooded Country is represented by a line of tiny tree symbols.

NatGeo_sm

Sometimes using green is just out of the question. If you want to use a range of colours to represent elevation (hyposgraphic tinting), having green forest is going to be quite confusing. In these cases I have I tried a technique of having a dashed green line at timberline, bordered by some fill on the downhill side, fill that quickly fades out. You can do this in QGIS by using shapeburst fill, shading to a set distance of a few millimetres.

McDonell_Lake_detail_sm

I have also played around with not marking timberline at all, and just putting a note beside the trail at the point when one would clear the trees.

OpalRidge_sm

Another option available to you if you have access to landcover data, is to give map-readers more information about how the forest makes that complicated transition to grassy tundra. In this case I used the Land Cover, circa 2000-Vector data available at Geogratis, and assigned progressively lighter colours to “coniferous dense” (which captures the main forest of spruce and fir), “coniferous open” and “broadleaf open” (which captures willow).

Seaton_sm

If timberline is something you just want to suggest, but don’t really need to accurately show, a method that can still look good is to style the digital elevation model in a series of fading greens. Have it become completely white at the elevation where timberline is typically encountered in the area. You get the effect of the “naked” mountains rising above forested slopes without introducing the complexity of avalanche tracks and the differences in where trees grow between north- and south-facing slopes.

RedRose_sm

Timberline in this area tends to be at 1500m

Sometimes the highest elevations on the map just touch timberline, in which case there can be a large zone where small meadows alternate with clumps of diminutive trees, an ecology often called parkland. I’ve tried representing this by scattering a host of little tree shapes, sort of trying to show how trees are still there, but not connected to the “mainland” of the forest.

QuickHills_sm

And this is just scratching the surface. The more you study timberline, the more you realize the folly of trying to show it accurately, yet the importance of indicating where we see it!

 

 

 

A new map of the Bulkley Valley

When I attended the ICA Mountain Cartography Workshop in Banff last spring, I was encouraged by a number of people there to consider printing and selling maps of my local area. Most of this last winter has been taken up by the production of this map, which was printed in April and is now available at Interior Stationary in Smithers, BC.Bulkley_Valley_poster_map_wordpressThere are a number of goals coming together here. From a cartography perspective, the idea was a map that would feature rich shaded relief generated in Blender. From a community perspective, the idea was to produce a map that represents the amazing topography of this area, that draws you in and makes you want to go exploring.

Every map is a story, and maps, being deliberately authored, contain bias. In this case, I wanted the story to be about the terrain — the mountains, rives and lakes — and my bias was to emphasize the romance of landscape at the expense of the technical ways we divide it up. So missing from this map are all those lines that chop up a landscape: town boundaries, ski area boundaries, recreation site boundaries, private land designations, First Nations reserves and Regional District subdivisions. Even provincial park boundaries got the axe, because while on the one hand a park indicates a piece of the landscape to be preserved from development, on the other hand is the implication that outside the boundary anything goes. Park boundaries on maps suggest that only within the line is the higher quality landscape. I wanted to avoid that suggestion.

As a concession to practicality, most roads are named and you can use it as a road map. But it’s not one of those maps where every road in the provincial database is present. I left out the vast majority of forestry roads, including only those mainline roads which are commonly driven. And here too bias plays a part, because although I’ve lived in the valley for 20 years, my notion about what roads are “commonly driven” will differ from someone else’s.

Bulkley_Valley_poster_map_detail2_wordpressAs another concession I put in some point markers for those small provincial parks, or recreation sites, where a person can camp or picnic. I did this because, like roads, these are important landmarks for people.

Trails are not shown on the map, partly because at this scale, 1:150,000, you can not use it as a trail map, but also because I didn’t want to suggest that trails are an important interpreter of the landscape. When you put trails on a map they stand out as a travel network, perceived in the mind not unlike a road network. We think that where trails go must be better than where trails don’t go. I didn’t want to bias the viewer in this way.

The colouring of the map is derived from land cover data, which is essentially a satellite or aerial photo that someone has looked at and classified into zones of different stuff. Coniferous and deciduous and mixed forest are all identified, as are ice and snow, bare rock, built-up areas and shrubland. I’m a big proponent of the idea that a map should faithfully give you the colours of a landscape before you ever arrive in the area, so the colours I chose were keyed to the summer landscape here — and consequently there’s a whole second possible project of a winter map of the valley. I think the colours work pretty well, although it’s something of an idealized summer landscape. For example, there are no lingering snowpatches such as one would actually see. It is quite clear how coniferous forests dominate upper slopes while the valley bottoms are full of cottonwood and aspen. You see how south facing slopes are different from north-facing. Given that it can’t account for how light changes throughout the day, it’s a pretty good representation of what we see.

Bulkley Valley detail 300dpiNaming is an interesting area in map-making. If you publish an article about how such and such peak should be named after your uncle Fred, people will agree with you or not, but you’ll be known as having proposed that name. However if a map-maker puts a name on a mountain or creek, no one really questions it. Maps are seen as authoritative.

But names can be seen as impositions on the landscape like other lines. Does it improve this river that we call it the Bulkley River? Would it be a better river if it was labelled the Wedzenkwe? Or is it best not labelled at all? I made a decision to go with the naming of features that reflects the British Columbia geographic names database — in other words, the names that appear on most maps and with which most map-readers are familiar — but I’m not entirely comfortable with this. For example, I’d like to see a version of this map with Wet’suwet’en and Gitxsan names on as many features as possible.

We have a lot of unnamed features in this area — or, I should say, features without official names. I hope that this map will act as a lightning rod for name information, that people will give me local names and I can add them on to future editions, and thus substantiate them.

Buffering (or haloing) text over complex backgrounds using the Screen blend mode

This is a common problem when you are working over a complicated, multi-colour background. Such backgrounds tend to swallow text!

Here’s an example, where text lies over a background with a lot of variability in value (darkness).text over complex background

Here’s the same image in greyscale, just to show the pixel values. Out of a total range of 0 to 255, the pixels here range from 6 (almost black) to 240 (almost white). Black text over light portions reads easily, but it’s hard to read the letters, M, N and T because of the way they overlap dark areas.value map of background

The classic, or perhaps I should say default solution, is to buffer the text in white. This works fine, in that you can read the text more easily, but it’s a crude solution and it’s a bit loud. It lacks subtlety. white 1mm buffer

A somewhat more elegant solution is to have the buffer match the background colour. In this example the text stretches across many background colours, so no matter what colour you select it’ll be a compromise. Still,  it looks better than white. The problem is that across the map as a whole each piece of text will probably get a different buffer colour, depending on what is dominant in its background.1mm colour buffer

What we really want is a way to pick up the background colour for each pixel, and colour the buffer that way. We can actually approximate this by using the blend mode of Screen.

Screen is the opposite of Multiply. Where Multiply transfers dark values onto another layer, Screen uses dark values to lighten another layer.

In this case, you set your buffer to something fairly dark, like 80% grey. Then set the blend mode of the buffer to Screen. You get this.screen 80 percent grey

Here the buffer colour echoes the underlying colour. The buffer around the T is orange-y, while the buffer around the O is grey. The buffer for the M uses both colours.

How would you do this in QGIS and Inkscape?

For text labels displayed in QGIS, this impressive piece of software can do this automatically. On the Buffering tab of the Labels dialogue, check Draw text buffer and specify an 80% grey for the buffer fill. (Note that 80% grey is RGB 51/51/51, HSV 0/0/20, or HTML #333333.)

Then set the blend mode to Screen. There are a couple things to note. One is that the sample shown will look ghastly; you can ignore that. The other is that the blend mode of the label is different from the blend mode of the buffer. The label itself probably has the default blend mode of Normal, and this can be checked on the Text tab.QGIS_buffer_screen

Here’s the result: Tiltusha example

In Inkscape, where you might be doing more complex text, text set on curved paths with adjusted kerning, you can also do this. Blend modes in Inkscape are applied to an entire layer, so you can’t give one piece of text a different blend mode than another. But by introducing a special layer that has a blend mode of Screen just beneath your text, you can put the buffers there.

The procedure goes something like this:

  1. Create a new layer below your text layer and set its blend mode to Screen.
  2. On the text layer, select your text and duplicate it with Ctrl-D. duplicate
  3.  Turn on Stroke for the duplicated text. (Text normally has fill but no stroke) and set the stroke colour to 80% grey. (You can do both of these steps simultaneously with a shift-click on the 80% grey swatch in the Palette at the bottom of the screen). Set its width as you see fit (1mm in this example). It should look pretty ghastly.buffer stroke on
  4. Press Shift-PgDown to send that duplicate piece of text to the layer below, the layer with blend mode of Screen. It should now look pretty nice. buffer moved to screen

I should point out one disadvantage of this two-layer approach: you can’t group the text with its buffer, a practice I normally do because it makes it easier to move labels around later.