Crafting Storytelling with Sankey Charts: A Guide to Creating and Applying Sankey Diagrams

Sankey charts, named after Mark Sankey, a South African mechanical engineer, are a powerful visual tool for displaying and interpreting flows from one set of values to another. Rather than just depicting the magnitude of the source and destination categories as a pie chart might, Sankey diagrams show how one set of things transforms into a slightly different set of things. With their unique ability to illustrate complex data flows and transformations in a visually compelling way, Sankey charts have become a staple in data visualization for illustrating processes, energy transfers, and financial flows. However, crafting a compelling Sankey chart requires not just technical skill but also an understanding of how to effectively tell a story through its flow and structure.

Understanding the Components of a Sankey Chart

A Sankey chart consists of several key components:

1. Nodes: Represents the categories or steps in a process. These are usually represented by rectangles or ovals and can have names or titles.
2. Links: Represents the flow between the nodes. These are typically shown as colored bars or ribbons. The width of these links is proportional to the magnitude of the flow—the wider the link, the greater the quantity.
3. Source and Destination Nodes: The nodes from which a flow originates and to which it flows, respectively.
4. Processes Indicated: The nature of the transformation or movement from one set of values to another.

Creating a Sankey Chart

1. Define Your Data: The first step is to ensure you have clean, relevant data that supports your story. This data can represent various types of flows, including but not limited to financial flows, energy transfers, or product recycling.
2. Organize and Visualize the Data: Sankey diagrams are best suited for large or complex datasets because they condense a lot of information into a single visual. However, be mindful of the level of granularity in your data to ensure clarity.
3. Choose Your Software: The best software depends on your personal or organizational preferences and technical expertise. R, Python, and Excel are popular options for creating Sankey diagrams. Each has its strengths and drawbacks, but all can produce effective visualizations.
4. Aligning Nodes and Links: For an effective Sankey chart, ensure the nodes are aligned to the left or right for better visual flow and readability. The links should be drawn in the direction of the flow, with the thickness of the links proportional to the size of the data entry.
5. Formatting Colours and Labels: Use color to highlight different types of data flow, and make sure your labels are clear and readable. Avoid cluttering the chart, and consider grouping similar processes together if they are numerous.

Applications of Sankey Charts

Sankey charts are useful across a broad spectrum of applications, including:

• Environmental Studies: To show the flow of water, energy, or carbon from one location or process to another.
• Economic Activity: For explaining the flow of money, resources, or products within an economy or industry.
• Energy Transfers: Analysing the flow of energy across different systems or processes.
• Supply Chains: Illustrating the flow of materials or products from suppliers to manufacturers to consumers.
• Healthcare Data: Showing the pathways of medical interventions or treatments from their source to their end point.

Crafting a Story

The true power of Sankey charts lies in their ability to tell a story about how one set of things transforms into another. When crafting a Sankey chart, consider the following:

• Alignment with Your Audience: Your audience’s familiarity with the data or process you’re visualizing should inform how much complexity you include and how you translate technical terms into relatable explanations.
• Communicating Change: If your story is about change over time, you can create a series of Sankey diagrams to show how the flow has evolved.
• Inspiration and Emotion: Crafting a narrative that evokes emotion can enhance your audience’s engagement and understanding, making them more likely to recall your key points.

In conclusion, Sankey charts are a versatile and compelling tool for data visualization, particularly for representing complex flows. By understanding how to effectively create and apply them, you can tell powerful stories that engage your audience and inform decision-making. Whether you’re explaining environmental changes, mapping out financial flows, or illustrating the complexities of a supply chain, Sankey diagrams can enhance your communication and help your audience see the flow of your data in a new, intuitive light.

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