Bridging the Flow: Unveiling the Artistry of Sankey Charts

Introduction

In an era where data visualisation is an indispensable tool for unraveling complex systems, Sankey charts stand out as a remarkable instrument for the visual exploration of the flow of materials, energy, or information. First conceptualised in 1898 by a Scottish mechanical engineer, Sir Mark Hall, Sankey diagrams have transcended the boundaries of their original application in thermodynamics. This article will delve into the world of Sankey charts, exploring their creation, their myriad applications, and why they have become an indispensable asset in the data viz toolkit.

What is a Sankey Chart?

A Sankey chart is a type of flow diagram used to visualize the quantification of material, energy, or cost flows. These charts are designed to track the flow within a system from initial supply at the source to final disposal at the end. They are visually compelling because they feature flowing lines that correspond to the magnitude of the substance or energy being transferred, often from a wider source to a narrower receiving point. This feature, known as “Sankey thinning,” allows the viewer to quickly understand the proportionate differences in quantities even at different stages in the process.

Creating a Sankey Chart

Creating a Sankey chart involves identifying the nodes (points or locations) within a network and the paths (flows) connecting those nodes. The following is a brief guide to the steps typically involved in creating a Sankey chart:

Define the System and Flow: Begin by outlining the system you want to visualize. Decide what the source and destination nodes are and the paths of flow between them.
Choose the Software: Select an appropriate tool for drawing Sankey diagrams, such as Microsoft Word and Powerpoint (with templates), commercial software like Sankey Illustrator, or open-source platforms like Gephi and Python libraries like NetworkX and Matplotlib.
Layout Nodes and Flows: Carefully position the nodes on the chart and draw lines that represent the flows. Ensure the width of each line is proportional to the magnitude of the flow.
Sankey Thinning: Adjust the width of the lines along the path to represent the change in the flow quantity between nodes. This is the “thinning” effect that separates Sankey charts from traditional flowcharts.
Final Touches: Add labels to the nodes and flows, include a legend, and refine the color scheme to enhance the readability and visual interest of the chart.

Applications of Sankey Charts

Sankey charts find application across a vast array of fields:

Energy Systems: Demonstrate how energy is converted and transformed in complex energy systems, such as power generation and use, providing insights into efficiency losses.
Environmental Engineering: Track different substances in environmental flows, contributing to an understanding of pollution patterns and material cycles.
Transportation and Traffic Analysis: Visualize the flow of vehicles, people, and goods through urban networks, helping urban planners and researchers mitigate congestion and improve efficiency.
Financial Reports: Illustrate the flow of funds through an organization or investment portfolios, allowing stakeholders to see where financial resources are allocated and returned.
Data Science and Analytics: Display the pathways of user interaction on websites or within computer systems, optimizing user experience and improving design.

Conclusion

The artistry of Sankey charts lies in their uncanny ability to encode and convey large amounts of data in a visually intuitive format. From elucidating complex processes to simplifying information for decision-makers, these diagrams are more than just a tool for visualizing data—they are a key to understanding it. As we continue to navigate the complexity of our systems and data, the Sankey chart remains an invaluable asset, a beacon in the realm of data viz, bridging the gap between the intricate workings of systems and their succinct representations.

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