Why does the sunlight come from the north in shaded relief maps? The sunlight in this map comes from the upper left, but in the northern hemisphere the sun mostly occupies the southern half of the sky, so why isn't it coming from below?

Aug 4, 2021 · 1:56 PM UTC

94
1,696
480
6,761
The reason cartographers place the sun in the north is because of a quirk of human perception that they are accounting for. To illustrate, take the following image. Do you see the lightest gray side as being on top of or on the bottom of a cube?
10
49
5
582
Most folks see the lightest gray side as the top of a cube. Why? Because as humans we tend to assume light comes from above. It is for this reason that cartographers light their maps with the sun positioned above the map, even if it wouldn't be there in reality!
7
29
3
591
Take the following example. Do you see the location marked by the "X" as a ridge or a valley?
7
14
4
453
Most folks will see that as a ridge, but it's actually a valley. If you follow the valley to the right, you'll see it run into a river, which appears to be sitting on top of another ridge. That ain't right!
4
7
1
404
Here's the same area, lit from the north instead of the south. The difference is remarkable isn't it? That same river running along the right now looks like it should: at the bottom of a valley. All we did was change the angle the sunlight was coming from.
5
20
2
680
As cartographers, we make maps for humans and this means paying attention to how our maps will be perceived. It's true, a map won't always have the sun in a realistic position, but that physical inaccuracy is made up for in a more important dimension: perceptual accuracy.
9
26
1
900
Replying to @mattparrilla
It’s graphical convention that lessens the possibility of relief inversion—where mtns look like valleys and vice versa. May have originated because most right-handed people place a desk lamp to their upper left when writing or drawing.
3
3
94
The above tweet is the first in a thread. Let me know what you think and thanks for sharing the map!
Maybe it doesn't represent the Earth. Think of it as a digital model of a physical model of the Earth in a digital model of a conference room. Imagine it mounted on an easel, lit by normal room lights…
1
10