I’ve written before about the problem of “rules” and “laws” in data visualization. A classic one is “Thou must start your axes at zero.” If you’re reading my Brinton blog, go see what he had to say about it)
In this post I want to dispel this myth. It’s a myth that’s close to my heart. In August 2009 I went on the record (by commenting on The Guardian’s Datablog) that I disliked one of their charts because their axes didn’t start at zero.
Let’s take the data from that Guardian article in order to investigate this Rule. Here’s how it looks with zero included:
This is bad for at least 4 reasons:
- It doesn’t really expose the change of the record over time.
- It especially doesn’t highlight the impact Usain Bolt had on the record.
- It doesn’t make great use of the space – there’s lots of dead space.
- It’s boring.
What happens when you break the rule?
All the problems are removed. It’s engaging, Usain Bolt’s impact is clear and it makes great use of space.
There’s one final reason not to include zero in this case. I do not know what the ultimate fastest time a human being will run 100m, but I can guarantee it isn’t zero seconds. My point is that not all measures you are charting have real zeros. In this case, the “zero” might be 9 seconds or so.
Once you learn the guidelines, you’ll be able to fine tune your charts by bending or breaking them according to your use case and objective. Sticking to the rules means you will satisfy the 5 criteria Alberto Cairo defines for a successful chart (he discussed these at his 2014 Tapestry Keynote):