Give me a reference point and I will tell you how bad your incidence is

a commentary on how one dispute about colors showed deeper problems with Corona maps

There was a little argument between two major German news media some days ago. It's related to Corona and data visualization and I have a clever answer, so hear me out or scroll fast. Still here? All right, let's do this:

The story is that Bild accused Tagesschau of showing manipulative maps of Covid incidence in German regions. Bild noticed that on one day Tagesschau published a yellow map, but months later they published a map with almost the same numbers but this time in red.

Illustration of Covid incidence maps of Germany in yellow and red color

Bild concluded that by choosing a scary color, Tagesschau tried to make the pandemic look worse (because politics). Tagesschau replied that one map version was actually for TV and the other for web and it just got mixed up. The story could end here. But there's a deeper problem...

Think: How can we in general tell if a number is small or big or scary or ok? It says nothing when a number is presented like "look, here's 1.5". We need a reference point such as "here's 1.5 and by the way it was 1000 the whole last year". Now we can tell something: 1.5 looks small.

So if a Corona map (like the Tagesschau's) wants to tell something about the incidence numbers... where is the reference point? What are we supposed to compare the numbers with to understand them? This might seem like a rhetorical question suggesting there isn't such point, but no, there is:

The reference point for a number in one region are the numbers in other regions. We can compare: Berlin — larger, Flensburg — smaller. Notice that it doesn't even matter if the map is yellow, red or say blue, as long as the shades differ. So reference problem solved? Not quite.

See, regional differences are not the only thing readers look for in the map. They also ask: "How is Germany doing as a whole country?" But in the Tagesschau map, a reference point to allow assessing Germany as a whole is missing. This is the core of the problem.

Illustration of reference points in Covid incidencemaps in Germany

The "how Germany is doing as a whole" information is represented by the average color of the map. But what can we compare this color to? 1) Other countries? Nope, there's just an ocean of grey. 2) The map from yesterday? Yeah, sure, do you remember it?

The only thing we can compare the average color of the map to is a cultural norm of which colors are considered good and which bad. But that's terribly vague and destined to cause disagreements; exactly like in the Bild x Tagesschau case.

Summary: Tagesschau (and others) show maps that are only good for comparing Covid incidence among regions and that fail to tell how the country as a whole is doing, because there is no reference point to which we could compare the average color; just a vague feeling of which colors are good and which bad.

Ideas for improvement? Glad you asked! 1) Show the neighbouring countries. 2) Show a change over time. 3) Cite a source that assesses the numbers (e.g. the health ministry, which already says which incidence numbers are good and which bad — that's the traffic light system).

Funnily enough, it's Bild who published a map that does this better as it seems to use the Corona traffic light colors. Now they just need to state explicitly that this is the source of the colors and the reference point to which the regional incidence numbers should be compared to.

Jakub Valenta

April 26, 2021