News and Notes from PolicyViz - Issue #4

Nov 02, 2021

Waterfall Chart Alternative?

Last week, a colleague asked me to look at some data about arrivals and departures. In each year, they knew the number of people that arrived at the company and the number that left the company, distinguished by race and gender. The graph we were discussing was a series of stacked bar charts that showed the number in each category for each racial and gender group.

It got me thinking about the Waterfall chart. I've always struggled with this chart type, not because I think it's hard to read, but because it's hard to make comparisons across different groups. Even a small multiples approach would be difficult to read, I think.

Furthermore, the basic Waterfall chart only shows the net change in each segment/year. Take this one, for example, using data I just made up. We start with 100 employees in 2015, add a net number of 7 employees in 2016, lose 8 the next year, and so on, until we have 130 total employees in 2021.

But is the "+7" in 2016 because we added 10 people and lost 3? Or did we add 100 and lose 93? That's likely important in certain cases, right?

So here's an alternative approach to the Waterfall chart, which shows both the gains and losses within each year instead of just showing the net gain or loss. I draw a horizontal line to connect the pairs of arrows that show the number of gains and losses in each year, with annotation above each just like in the standard chart.

The first version essentially uses the same span along the vertical axis, going from 0 to 160. But can we start the graph at something other than zero? This is no longer a bar chart--although the arrows sort of act like bars, don't they?--so we can change the axis, here from 80 to 150. You see the detailed changes more clearly here, but I'm not certain that cutting the vertical axis in this way is okay or if it overemphasizes the changes.

Anyways, this is just some thoughts on the Waterfall chart. If you have your own take or alternatives, please let me know. You can DM me on Twitter or contact me through my website.

As always, enjoy a smattering of other links and materials below.

Thanks for subscribing,

Jon

PolicyViz Podcast with Rebecca Pazos

Rebecca is a mum of one and a senior data journalist with The Straits Times for six years. Recently, she completed her Masters in visual tools with the University of Girona. She is dedicated to telling compassionate, human-centered data stories. We talk about her data journey, her work, and the make-up of the Times' graphics team.

Making a graph from the New York Times in Excel

I often show this annotated bar chart from the New York Times in my data visualization classes and workshops. A couple of weeks ago, a participant asked whether this could be built in Excel, specifically the alternating colors for the groups of bars. Well, that part is easy--adding all of the annotations is the real challenging and fun part! Check out the blog post and step-by-step Excel tutorial on YouTube.