I’m often asked by colleagues and students, “what makes a good data visualization?”. I believe data visualizations (and any data analysis) are story telling tools. As such, I have two criteria when I create or evaluate them:
- (1) The visualization should only have one main pattern it tries to convey. There is a tendency to create very complex and multi-faceted visualizations. However, stories are told one plot point at a time. Similarly, visualizations should each focus on one pattern at a time within a larger narrative.
- (2) Ignoring all labels and text, the pattern should be immediately noticeable. The value of the visualization is in serving as an aide to highlight an otherwise obscure pattern. Thus, a good aide should make the pattern painstakingly obvious and universally evident.
This may seem limiting, but I believe that even complex patterns can be elicited from good data visualizations within a few seconds. TED talks by Hans Rosling and David McCandless excellently demonstrate this power.
One of my favourite examples, and one of the most famous early examples of a data visualization, is by Florence Nightingale (read more here). Her visualization, printed below, helped showcase the need for hospital sanitation.
Let’s examine Florence Nightingale’s graph under my two criteria:
Ignoring all text, I immediately see a lot of blue. That blue area represents the number of deaths from preventable or mitigable diseases. This indeed is the pattern Florence Nightingale wished to highlight – a lot of soldiers were dying unnecessarily. Thus, this is an effective visualization of the data and helps tell a story.
Although we could have also examined a data table to arrive at the same conclusion, it is much less dramatic and perhaps a harder pattern to see. This is the power of a good data visualization – it presents patterns in numbers with colours and shapes, broadening prospective audiences’ ability to consume the information at hand.
We owe a great debt to innovators like Florence Nightingale and can strive to exemplify her creativity when we present the stories contained in our data sets.
I like to imagine the conversation Florence Nightinghale had after she created this visualization went something like this:
- General: I don’t see why we need to waste time and money cleaning the hospital
- Florence: Do you see all that blue?
- Army General: Yea…
- Florence: That’s how many soldiers we could have saved if we had clean hospitals
- General: We’ve got to do something about that blue! How much time and money do you need to clean the hospital?