Your flow should… flow!

A few weeks ago, a reader sent me his dataviz project, asking if it could join my Dataviz Inspiration project.

It was great. And it featured something I couldn't stop looking at: an animated Sankey diagram.

It got me thinking about how we visualize flows, and where dataviz is heading on the topic. So that's what today is about!

Chart types for flow

In case you've never bumped into it: I'm the author of Data To Viz, a classification of chart types built as a decision tree. If you head to the "flow" section, you'll see a list of chart types for representing flows:

Plenty of options. Their pros and cons aren't the topic today (but I strongly encourage you to explore them!). Here's the thing: they all share the same problem. And we can fix it.

The problem: where does the flow go?

Talking about flows reminds me of one of my favorite graphs ever added to the R Graph Gallery: a chord diagram of migration flows.

It's stunning — there's so much information packed in here. But I have to be honest: I had to stare at it for ages to decipher it. The main issue? Nodes are linked by chords, but it's hard to tell whether the flow goes from A to B, or from B to A.

The solution: flow must flow

We're in 2026. The vast majority of graphs we build are read on a screen, not on paper. So why not make the flow… actually flow?

Which brings me back to that reader's project: a Sankey diagram where every link has little dots animating along it, mimicking the direction of the flow.

I love it. 😍 It makes the graph feel alive, and it makes one thing instantly obvious: a quantity of something is moving from one entity to another.

It used to be tough

Building this kind of graph used to be a real struggle. First, you needed a technology customizable enough to create an animated shape like this — namely D3.js. Second, you had to build the animation itself. Not a piece of cake. (You don't want to know how long I spent on the animated connections of my Productive R Workflow landing page 😅.)

Back when I worked at Datadog, I helped a tiny bit on the Service Map: a network diagram with flows that animate on hover. It worked beautifully and was used by thousands of customers every day to drive decisions.

The code, though? Phew. Hard to follow! 😅

A bright future?

We're living in a new dataviz era now — one where AI removes the technical complexity from our projects. Our design eye and our inspiration should become the only things that dictate what we create!

I often talk about my AI skepticism (like last week). But there's one thing that genuinely makes me glad, and it's the reason I'm still writing about dataviz today: I believe AI is going to push our graphs to the next level. And I do love good graphs. 🤓

So, what do you think? Will you try to make the flow flow next time? Let me know.

See you next week,
Yan