Sankey Charts: How to Tell a Flowing Story with Your Data

Introduction

If you’re looking for a way to show how data moves from one stage or category to another, then Sankey charts are your new best friend. They’re not as well-known as bar charts or line graphs, but when it comes to visualizing flow, they’re hard to beat. Imagine you’re tracking energy usage, budget allocation, or even user behavior—Sankey charts can beautifully illustrate how resources, people, or actions flow through a system.

Sankey charts aren’t just about showing quantities; they’re about showing how those quantities break down and transition between stages. In this post, we’ll break down how to create and use a Sankey chart, along with some examples of when and why you should use one.

What is a Sankey Chart?

A Sankey chart is a flow diagram that uses arrows or paths of varying thickness to show how resources, quantities, or data flow from one category to another. The width of each arrow represents the proportion of the data it is carrying, so larger arrows signify larger flows.

Think of a Sankey chart as a map for your data, showing you how things move from point A to point B, and what happens in between.

Key Components of a Sankey Chart

To understand a Sankey chart, it’s important to know its core components:

• Nodes: These represent the categories or points where data enters or exits. Each node is a specific step or category in the process you’re illustrating.
• Links (or Flows): These are the lines or arrows connecting nodes. The size of these links reflects the volume of data moving between nodes. Thicker arrows show larger flows.
• Direction: A Sankey chart flows in a specific direction, usually left to right, showing how data moves across categories or steps.

When Should You Use a Sankey Chart?

Sankey charts are particularly useful when you need to show how something flows through a process. Some of the most common use cases include:

• Energy Flow: Visualizing how energy is produced, transferred, and consumed in different sectors.
• Budget Allocation: Showing how a total budget is divided into categories and how much goes toward each expenditure.
• Customer Journeys: Mapping how customers move through different stages of a funnel, such as website visits, purchases, and repeat business.
• Traffic Flow: Displaying how visitors navigate from one webpage to another within a site.
• Supply Chain Analysis: Showing how goods move through various steps in a supply chain from raw materials to final product.

In any scenario where you’re looking at a process with multiple steps, and you want to show both the quantities involved and how they move between stages, a Sankey chart is a great option.

Why Sankey Charts Are Powerful for Storytelling

A Sankey chart is more than just a flow diagram; it’s a visual storytelling tool. The strength of a Sankey chart lies in its ability to show movement while also emphasizing proportions. This makes it perfect for helping audiences understand the importance of each flow in relation to the whole system.

Here’s how Sankey charts enhance storytelling:

• Visualizing the Whole and the Parts: You can show the big picture (e.g., total energy consumption) while also breaking it down into individual parts (e.g., how much energy is used by each department).
• Showing Complexity Clearly: Sankey charts handle complex datasets with ease by organizing them into flows, making it easy to trace data from one category to the next.
• Highlighting Key Movements: By varying the thickness of flows, you can immediately draw attention to the most significant parts of your data.

Creating an Effective Sankey Chart

A Sankey chart can seem intimidating at first, but creating an effective one is all about focusing on simplicity and clarity. Here are some tips to help you create a Sankey chart that tells a clear and compelling story:

1. Identify the Flow You Want to Show

Before creating a Sankey chart, clearly define what flow you want to visualize. Are you showing the distribution of energy, the allocation of a budget, or the movement of website visitors? Having a clear objective will help guide your design decisions.

2. Group Categories Thoughtfully

Sankey charts work best when categories are logically grouped. Make sure your nodes (the categories where the data enters and exits) are clearly labeled and easy to understand. You don’t want too many nodes, as this can overwhelm your audience and make the chart difficult to read.

3. Use Consistent Scales

The size of the arrows should be proportional to the flow they represent. Make sure that the chart maintains consistent proportions, so it’s clear which categories are carrying more or less data. Misrepresenting the size of arrows can confuse or mislead your audience.

4. Keep It Simple

While Sankey charts can handle complexity, you don’t want to overcrowd the visual with too many nodes or flows. Focus on the key flows that are important to your story. It’s better to leave out unnecessary details than to overwhelm the viewer.

5. Highlight Key Insights

Use color or annotations to draw attention to the most important flows in your chart. This will help guide your audience’s eyes to the insights that matter most.

Examples of Sankey Charts in Action

1. Energy Flow Diagram

One of the most famous uses of Sankey charts is in energy flow diagrams. Imagine a chart that shows how energy is sourced from different types (solar, coal, nuclear) and how it flows to various sectors (residential, industrial, transportation). The thickness of the arrows helps to visualize which sectors consume the most energy.

2. Budget Allocation

In a company budget, a Sankey chart can show how total revenue flows into various departments such as marketing, HR, and operations. It can also show how each department’s budget is further divided, for example, how much of the marketing budget is spent on digital ads versus events.

3. Customer Journey on a Website

A website owner might use a Sankey chart to track how visitors move from the homepage to other pages, showing where visitors drop off or convert. The chart would show the flow of traffic from one page to another, with wider arrows representing pages that receive more visitors.

Common Mistakes to Avoid with Sankey Charts

While Sankey charts can be a great way to visualize data, there are a few common mistakes to avoid:

• Overcomplicating the Chart: Too many nodes or flows can make the chart hard to follow. Focus on the most important data flows to keep things simple.
• Inconsistent Flow Sizes: Make sure the width of each flow is accurately proportional to the data it represents.
• Lack of Context: Always include labels and a clear title to provide context for your chart. Your audience needs to understand what the nodes and flows represent.

Conclusion

Sankey charts are a fantastic way to visualize flows in your data, whether you’re tracking energy usage, budget allocations, or customer journeys. By focusing on simplicity and using clear visual cues, you can create a Sankey chart that not only informs but also tells a compelling story.

Ready to get started with Sankey charts? Try one of the tools mentioned above, and start transforming your data into powerful, flowing visuals!