Sankey charts are a type of data visualization that effectively display the flow and magnitude of data, making it easier to understand complex systems. Also known as Sankey diagrams, these charts have been used for centuries but gained a resurgence in popularity due to advancements in data visualization tools and the increasing complexity of data being analyzed.

What are Sankey Charts?

Sankey charts are a visual representation of flows or networks, where each arrow represents the flow of data from one category to another. They are named after Captain Matthew Henry Phineas Riall “Sankey”, a British engineer who used this type of diagram to visualize the energy usage of his factory as early as 1898.

Sankey charts combine elements of graph theory and flow maps, displaying information as a set of interconnected nodes connected by arrows or lines. The width of these lines corresponds to the quantity of data they represent, making it easy to see which parts of the system have the highest or lowest throughput.

Key Components of a Sankey Chart

1. Sources and Sinks:

• Sources are categories or states from which the flow begins, often displayed on the left side of the chart.
• Sinks are categories or states where the flows end, usually positioned on the right-hand side of the chart.

2. Flow Lines:

• These are the connecting lines between sources and sinks, representing the movement of data.
• Each line’s thickness indicates the volume of flow, with thicker lines showing larger amounts.

3. Paths:

• Straight Paths show direct flows.
• Curved Paths might be used to avoid overlap, enhance visual comprehension, or indicate indirect flows.

4. Labels and Legends:

• Labels typically include node names, and sometimes flow amounts and values for clarity.
• Legends provide information on color coding, flow interpretation, or specific values used in the visualization.

Creation and Applications

How to Create a Sankey Chart?

Creating a Sankey chart typically involves these steps:

1. Data Preparation: Gather the necessary data on the categories and values of flows you wish to visualize.
2. Choosing a Tool: Select a data visualization software that supports Sankey charts, such as Microsoft Excel, Tableau, R (using libraries like “diagram” or “ggraph”), Python (using libraries such as “NetworkX” or “plotly”), or specialized visualization tools like Sankey.js.
3. Mapping Flows: Input the data and specify which categories correspond to sources and sinks. Assign values to the flows and set a color scheme if desired.
4. Layout and Style: Adjust the positions, orientations, and styling options to ensure the chart is understandable and aesthetically pleasing, avoiding clutter and overlapping elements.
5. Customization: Enhance the chart’s readability with labels, legends, and annotations for greater context.
6. Review and refine: Check for correct data representation, coherence, and update the chart accordingly.

Applications of Sankey Charts

Sankey charts find application in wide-ranging sectors and scenarios:

1. Energy Systems

• Tracking energy generation, distribution, and consumption, showing flow efficiency or inefficiencies.

2. Business Processes

• Mapping internal business processes, highlighting operational bottlenecks or inefficiencies.

3. Supply Chain Analysis

• Visualizing goods flow within supply chains, identifying major suppliers or product distribution patterns.

4. Financial Markets

• Displaying financial flows between assets, markets, or sectors to identify trends and interdependencies.

5. Environmental Studies

• Modeling the flow of materials in ecosystems, assessing the impact of pollution and resource usage.

6. Social Dynamics

• Visualizing information or resources flow among social actors, exploring communication patterns or influence networks.

Conclusion

Sankey charts facilitate the comprehension of complex flow networks and systems by presenting data in an intuitive, visually appealing manner. Their ability to handle large quantities of information and their adaptability across various industries make them a valuable tool for decision-making, process optimization, and system understanding. As data visualizations continue to evolve in detail and interactivity, Sankey charts are poised to play an increasingly critical role in managing and understanding complex systems.

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