Sankey charts are a type of data visualization that can be used to depict the flow of materials, energy, or information between different entities. These charts are particularly useful for visualizing complex and multidirectional flows, making it easier to understand the relationships and patterns within a dataset.

In this article, we’ll explore the concept of Sankey charts, delve into their creation, and discuss some of the most common applications in various fields such as science, economics, and energy studies.

What are Sankey Charts?

Sankey charts are named after Captain Matthew “Tol” Sankey, who developed this type of graph in 1898. Unlike traditional chart types with a single data axis, Sankey charts consist of nodes and flows. Each flow is shown by arrows with varying thickness, reflecting the magnitude of a quantity transferred between the nodes, or points of interest.

Sankey charts have several key features that make them uniquely suited for specific use cases:

1. Visualization of Flow: They emphasize the flow direction and volume between sources, sinks, and intermediate points.
2. Complex Relationships: They are excellent for showing intricate connections and systems, such as energy usage by different sectors or transportation networks.
3. Highlighting Importance: By the width of the arrows, one can easily see which connections are more significant in terms of quantity or other relevant metrics.
4. Compact Representation: Sankey diagrams can convey a large amount of data in a compact visual format, making them suitable for reports and publications.

How to Create a Sankey Chart

Creating a Sankey chart can be accomplished using a wide range of software tools and programming libraries. Some popular options include:

Web-based Tools:

1. Sankeyviz: A JavaScript library specifically designed for creating Sankey diagrams. It is highly customizable and works well in web applications.
2. D3.js: A powerful JavaScript library for data-visualizing and can be used to create custom Sankey diagrams with full control over styling and interactive elements.
3. Visualize This: An online tool that lets you interactively build Sankey charts without coding knowledge.

Desktop and Dedicated Libraries:

1. R: With libraries like sankey, networkD3, and RGraph::Sankey, you can easily create Sankey diagrams using this popular language for statistical computing.
2. Python: Libraries like plotly, networkx, and SankeyGraph offer functionalities for creating interactive and publication-ready Sankey charts.
3. MATLAB: A MATLAB-based toolbox includes functions for creating Sankey diagrams, making it a preferred choice for many engineers and researchers.

To create a basic Sankey chart, follow these general steps:

1. Prepare Your Data: Gather the source, target, and flow data, usually in the form of source-target pairs and the corresponding values or categories.
2. Select a Tool: Choose the tool that best fits your needs, considering factors like your technical skill set, data format, and the level of interactivity you want to achieve.
3. Design Your Chart: Use the tool’s interface or write code to map your data onto the nodes and flows of the chart.
4. Customize and Style: Adjust the visuals, color schemes, and other design elements to enhance readability and aesthetics.
5. Analyze and Present: Review the chart for accuracy and clarity, ensuring it effectively communicates the intended message. Use the chart to support your analysis or presentation.

Applications of Sankey Charts

Sankey charts find utility in various domains due to their ability to convey complex flow narratives in an intuitive way. Here are some common applications:

Energy Economics

Sankey charts are widely used to illustrate energy flows, showing where energy is produced, consumed, and transformed across different sectors. For example, they can depict trends in renewable energy sources and their impact on overall energy consumption patterns.

Environmental Science

In environmental studies, Sankey diagrams can represent the movement of pollutants, nutrients, or resources through ecosystems or from industry to the environment, helping researchers and policymakers to understand impacts and guide conservation efforts.

Transportation Systems

Transportation planners use Sankey charts to display traffic flows, cargo movement, or public transit usage, showing how different modes of transportation connect and interact. This information is crucial for optimizing routes, understanding congestion, and planning infrastructure improvements.

Business Analysis

In business settings, Sankey charts provide insights into supply chains, sales channels, and customer journeys, aiding in strategic decision-making, identifying bottlenecks, and improving operations.

Public Health

Public health agencies use Sankey diagrams to track the transmission of diseases, showing how different factors such as demographics, travel, and healthcare interactions contribute to infection rates. This visualization helps in the development of targeted interventions and policies.

Information Technology

In IT, Sankey charts are used to depict network topologies, data flows, or resource allocation within IT systems, revealing inefficiencies, potential bottlenecks, and opportunities for optimization.

Conclusion

Sankey charts offer a visually engaging and informative way to tell stories about process flows, making them valuable both analytically and pedagogically. By mastering their creation and understanding their applications, professionals across various fields can leverage this data visualization tool to uncover insights, make data-driven decisions, and communicate complex information effectively.

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