Raising relief maps from a line chart

Jack Goodall

Hello! I’m Jack, a developer on the app team. Datawrapper offers lots of great mapmaking options — but this week I want to try making maps using our line charts, something they definitely weren’t intended for.

The inspiration for this Weekly Chart came from looking at some raised relief maps. I’ve always loved how this type of map gives you an intuitive feeling for the shape of the land, and also just looks good when framed and hung up on a wall.

I wanted to see if I could use Datawrapper to replicate this intuitive representation of elevation, hopefully with results that also look good enough to be used as decoration.

The obvious limitation was that my plot would need to be displayed on a screen, without that handy third dimension. However, we can simulate depth using perspective:

(Be warned: Depending on the device you’re reading this on, the large number of lines in these maps may slow down your browser considerably. This isn’t what our line charts were built for!)

I’m very satisfied by how three-dimensional these maps look, especially when changing the height of the plot, which makes it look like the you’re changing the angle at which you’re viewing the scene. Try it yourself by clicking "Edit this chart" in the top right of one of my maps, then dragging the bottom of the plot up and down in the "Visualize" step.

I created these maps using Open Elevation’s self-hosted API:

• First I set the bounding coordinates of the area I wanted to map.
• I then collected the elevation of about 100,000 points distributed in a 150x700 grid over that area.
• I formatted my data by grouping one latitude value per column and one longitude value per row. This allows me to plot one line on my map per line of latitude.
• For each cell on the map, I set a value equal to the latitude + elevation at that point.
• The elevations are scaled down depending on how big the mapped area is, so that the peaks and valleys look good and clear.

The main issue with this approach was that the landmasses were very hard to make out from the sea surrounding them (since the Open Elevation API also returns 0 elevation for coordinates that are in the ocean).

To address this issue I split each line of latitude into two, with one line representing the sea and the other the land. This allowed me to color and style them differently in Datawrapper to make the landmasses stand out.

This method still isn’t 100% accurate, since any point with an elevation of 0m is treated as sea, which isn't necessarily true. Ideally we would use the true coastlines of the landmasses to determine whether a point is land or sea.

For even cooler maps, we could include bathymetric data of ocean depths to visualize the sea floor as well. I’ll leave that as an exercise to the reader, or maybe a future Weekly Chart!

While creating these maps I was reminded of the album art for Joy Division’s Unknown Pleasures, which our visualization developer Ivan has recreated in a previous Weekly Chart — it’s definitely worth a read if you enjoyed this article. Check in next week for a new Weekly Chart from our writer Rose.

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Jack Goodall

(he/him) is a software developer in Datawrapper’s app team. He’s keen on squashing bugs and optimizing performance. When he’s not clacking away at his keyboard, he enjoys skiing, photography, rock climbing, and twiddling his mustache. Jack lives in Lyon.

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