Streamlined Visual Narratives: The Art & Science of Sankey Diagrams

Introduction

In today’s data-driven world, the ability to present complex systems and processes clearly and compellingly is integral to successful data analysis, education, and communication. One such visual tool that has gained popularity across various fields is the Sankey diagram. This innovative graphing style allows for a visually intuitive representation of flows of materials, energy, or work within a process, making it an invaluable tool for understanding intricate systems. This article delves into the art and science behind Sankey diagrams, how they can be created, and their diverse applications.

What is a Sankey Diagram?

A Sankey diagram, named after the 19th-century engineer Ernst Eduard Heinrich Sankey, is a directional, flow diagram showing the quantity of materials, energy, or cost etc. moving through a process. These diagrams typically consist of arrows that converge at nodes, where materials or energy enter, exit, or are transformed.

Sankey charts are distinguishable by their width: the flow of material is made proportional to the amount of product or energy moving along the arrows. This characteristic makes Sankey diagrams an effective way to represent the efficiency of flows or systems at a glance, highlighting both energy-saving opportunities and bottlenecks.

The Art of Sankey Diagram Creation

Crafting a Sankey diagram is as much an art as a science. Here’s how to approach the process:

1. Define the Objective: Begin by clearly defining the purpose of your Sankey diagram. What data flow are you trying to represent? What aspects of the system need to be emphasized? This will impact the design choices you make.

2. Select Appropriate Software: Once you have a clear objective, choose the right tool for creating Sankey diagrams. There is a variety of software available, such as Sankey++ by Jürgen Koschier, which is free, and more advanced tools like Gephi, Power BI, or professional design software like Adobe Illustrator.

3. Gather and Organize Data: Collect your data in a format ready for visualization. Sankey diagrams often require data in a hierarchical structure where each step is a level lower than the step before it.

4. Determine Arrow Shapes and Widths: Assign shapes and widths to the arrows based on your dataset. Larger widths represent higher flows, and smaller widths represent lower ones.

5. Design the Layout: Utilize the properties of your chosen software to arrange the nodes and arrows in a logical and organized flow. Sankey diagrams are most effective when the flow makes intuitive sense to the audience.

6. Ensure Clarity and Simplicity: Use clear labels and colors to make the information accessible. Avoid clutter by limiting the number of variables and keeping the visual streamlined.

The Science of Sankey Diagrams

Behind the art lies the science of Sankey diagram fundamentals. Key principles in creating accurate and visually effective Sankey diagrams include:

• Consistency in Flow Direction: Maintain a consistent direction of flow, as reversing the direction of any arrow can significantly alter the interpretation of the diagram.

• Scale and Proportions: Scale the diagram proportionally so the widths of the arrows convey the magnitudes of the flows accurately.

• Efficiency and Balance: Balance the diagram so that it is visually appealing and avoids misleading the viewer. The balance between the efficiency of the flows and the readability of the diagram is a significant challenge.

Applications of Sankey Diagrams

Sankey diagrams are versatile and can be used in a range of industries:

• Engineering and Technical Analysis: Engineers use Sankey diagrams to evaluate and improve energy efficiency, material flows, and production processes within plants and manufacturing facilities.

• Environmental Assessment: Environmentally conscious organizations may use Sankey diagrams to illustrate the environmental impact of products or processes, from sourcing to waste generation.

• Urban Planning: Planners could create Sankey diagrams to visualize different flows: transport of people or goods, water distribution, or even information flow within a city.

• Economic Analysis: They can be used to map trade flows, investment patterns, or even the flow of resources and services within an economic system.

Conclusion

Sankey diagrams are an elegant synthesis of art and science, offering a unique way to visualize the flow of information, material, energy, or cost. By following the principles of design and data presentation, one can create clear and compelling Sankey diagrams that tell a story in a glance. Whether for technical analysis, education, or strategic planning, Sankey diagrams are powerful tools to demystify complexity and communicate information clearly and efficiently.

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