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Nikos hates pie charts

Nikos Fairburn, our Head of Operations, has a thing for pie charts, like the one we use to show the renewable electricity generated in New Zealand each month.

Nikos hates pie charts

To get to the bottom of his anxiety we gave Nikos a good listening to. Here’s what we learned.

A good pie chart shows a ‘part-to-whole relationship’. Pies, like pie charts, can be sliced in various ways to show ratios in quarter, half, three quarter slices etc.

But it’s not always easy to see how much each slice represents. 

Here is a pie chart with six slices. See how simple it is to determine the green slice is 25%, one quarter of the pie.

Chart 1 (Updated)

Now notice how the green slice isn’t as easy to recognise as 25% in the chart below.

Pie Chart 2

The man who invented the infographic; Edward Tufte, also had a thing for pie charts. 

He said ‘the only thing worse than a pie chart is several pie charts’ ¹, because ‘the viewer is asked to compare quantities located in spatial disarray both within and between pies’. 

Look at the pie charts below and you get the idea.

Pie Chart 3

Here’s the pie chart that got Nikos’s attention. Our carbon tracker shows the difference between various sources of electricity generation.

Pie Chart 4

Like the pie charts Edward Tufte takes exception to, it might not be the best way to display this information.

The amount of power generated in New Zealand, and the source of this generation, changes month to month. We like to keep track of this to show how close we’re getting to becoming 100% renewable and the mix of resources that supply electricity to everyone in New Zealand; hydro, geothermal, wind etc.

What’s missing from our pie chart is the amount of spare capacity — the power that could be generated or used but isn’t needed on any given month.

This new bar chart shows all of the resources and how much of the total amount of energy consumed they contribute, as well as the total amount of unused capacity.

New chart

It’s a small improvement to keep our customers better informed and help us understand the potential to transition from fossil fuels.

We hope you, and Nikos, like it. 

¹ The Visual Display of Quantitative Information, Graphics Press, 1983, p. 178.

Published on 16th February 2023
Nikos Fairburn
Nikos FairburnHead of Operations

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