Sankey charts are a type of flow diagram that can help us understand the movement of quantities from one point to another. They are often used to represent materials, energy, or data flows in a range of fields, including economics, engineering, and data visualization. Their ability to show complex flows in a visually intuitive manner makes them an excellent tool for uncovering insights and telling compelling stories through data.
In this article, we’ll explore the power of flow and delve into the creation and applications of Sankey charts, revealing how they can help unleash hidden insights and enhance your understanding of complex data.

What Are Sankey Charts?

Sankey charts, named after Captain Matthew Henry Phineas Riall Sankey, who invented the first iteration of the chart in the late 1800s, are a visual representation of flow or movement. They represent the distribution and flow of a quantity between different sources and destinations, often showing the magnitude of each flow. The width of the arrows or bands in the chart corresponds to the quantity of flow, with thicker or wider bands representing higher flows.

Key Components of Sankey Charts

To create a Sankey chart, you need to consider several key components:

1. Nodes: These are the starting or ending points of the flows, typically represented as rectangles, circles, or stars. Nodes can represent categories or specific entities, such as products, materials, or data sources.
2. Links (Bands): These represent the actual flows between the nodes. Each link connects an origin node to a destination node, displaying the quantity of flow in visual form. The width of each link indicates the volume of flow, with thicker links representing higher flow volumes.
3. Text Labels: These provide context and additional information about each node or the flow between nodes. Labels may include specific values, symbols, or other details that help in understanding the specific flows represented in the chart.
4. Orientation: Sankey charts can be oriented horizontally or vertically, depending on the preference or space available for the visualization.

Creation of Sankey Charts

Creating a Sankey chart involves several steps, which may vary slightly depending on the software, tools, or programming languages you use. Here’s an overview of the general process:

1. Data Preparation: Gather the necessary data for the Sankey chart. This typically includes values for the flows between each pair of nodes, along with information about the origin and destination nodes. The data can be organized in a tabular format with columns containing source node IDs, destination node IDs, and flow volume values.
2. Choosing a Tool: Select a tool or software that can create Sankey charts, such as Microsoft Excel, Google Sheets, Tableau, or programming libraries like Plotly for Python or D3.js for web applications.
3. Creating the Chart:
   • In Excel or Google Sheets:
     • Use the built-in chart types and customization options like shapes, colors, and layout.
     • Import or paste the data into a new sheet.
     • Choose the Sankey chart type from the chart selection menu.
     • Customize the chart’s layout, node labels, and link appearance using the formatting options.
   • In Tableau:
     • Drag and drop node and link data fields into the visual canvas.
     • Use Tableau’s built-in chart types and customization options to create your Sankey chart.
     • Customize the chart by adjusting colors, labels, and tooltips.
   • In Python using Plotly:
     • Install the Plotly library.
     • Import your data into a pandas DataFrame.
     • Use Plotly’s library to create a Sankey graph, passing the necessary data fields (source, target, value, node labels) as parameters.
     • Customize the graph’s colors, layout, and appearance using Plotly’s API.

Applications of Sankey Charts

Sankey charts find applications across various fields and industries, including:

1. Economic Analysis: Sankey charts are useful for visualizing the flow of resources, such as money, goods, and services between countries or sectors in a national economy.
2. Energy Industry: They can be used to show the flow of energy sources (e.g., coal, oil, and renewable energy) to power plants, and then to consumers, illustrating the efficiency and distribution patterns.
3. Data Science: In data science, Sankey charts can help visualize the flow of data through various stages of a machine learning pipeline, showing where data is gained or lost at each step.
4. Healthcare: In healthcare, Sankey diagrams can depict the flow of patients through different departments or treatments, tracking the progression of disease cases or treatment outcomes.
5. Environmental Science: They can illustrate the flow of materials (e.g., water, pollutants, and gases) from sources to sinks, showcasing environmental impact and remediation measures.

Conclusion

Sankey charts are a powerful visualization tool that can shed light on complex data flows and relationships. By leveraging their ability to represent the magnitude and direction of flows, Sankey charts enable a deeper understanding across diverse fields. Whether creating charts manually or using specialized software, the techniques discussed in this article provide a foundation for effectively visualizing and communicating flows in your unique datasets.

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