Visualizing Flows with Sankey Charts: A Comprehensive Guide

Sankey diagrams, named after Captain Sankey’s 1898 report on energy conservation, are a powerful tool in visualizing the direction and flow of data between different entities or stages. They are particularly useful in representing energy or materials flow, data transfers, and economic flows among other applications. In this comprehensive guide, we explore the creation of Sankey charts, their application areas, and how they can help in understanding complex data flows visually.

Understanding the Basis of Sankey Charts

A Sankey chart is a graphical representation of a flow or transfer process, showing the direction, quantity, and, in some cases, the cause and effect of the flows. It’s designed to visually communicate the distribution of data among multiple categories. Sankey diagrams are organized in a systematic way, with the width of each flow representing the magnitude of the data, making them easier to interpret and understand.

Essential Aspects of Sankey Charts

Layered Structure

Sankey diagrams are composed of a series of interconnected layers, or nodes, connected by arrows. Each arrow or flow represents a unique direction within the data flow. The width of the arrows can vary based on the volume of data or quantity being represented.

Node and Link

• Node: Represents any starting or ending point of a data flow.
• Link: Represents the flow of data between nodes, and their width reflects the data quantity.

Severity and Color

In addition to width, Sankey diagrams can incorporate color coding, highlighting different categories. This helps in distinguishing flows based on their origin, destination, or characteristics, enhancing the overall clarity and comprehension of the visualization.

The Art of Creating Sankey Charts

Step 1: Data Preparation

Start by plotting your data in a spreadsheet or data table format. Break down your data into two types – the input and output categories for each node, and measure the amount of flow between any two nodes.

Step 2: Assign Colors or Gradients

Decide on the colors or gradients to apply to your Sankey chart. For a professional look, it’s best to follow color trends and select colors that are easy to distinguish and aesthetically pleasing.

Step 3: Software and Technology

While there are several tools and programs that can help you create Sankey diagrams, software that supports customizability and simplicity, such as Tableau and Python libraries like matplotlib and plotly, are highly recommended.

Step 4: Layout Planning

When laying out your Sankey diagram, start by deciding on the width of your diagram and a suitable scale for your data. Arrange your nodes and links carefully to ensure clear visual flow and minimal overlap for better reading.

Applications of Sankey Charts

Sankey diagrams are versatile and can be applied in various fields:

1. Energy and Power Systems: Show how energy is converted from one form to another within a system or across different systems.
2. Economic Flows: Visualize the flow of money and economic activities from one sector of the economy to another or between countries.
3. Data Distribution: Represent the flow of data between systems, databases, or even personal information flows.
4. Environmental Studies: Analyze the flow of resources or pollutants from different sources.
5. Software Engineering: Illustrate data transfer between software components or data analysis flows.

Conclusion

Sankey diagrams are a valuable tool for visualizing complex data flows, making them easily comprehensible and engaging. Whether you’re analyzing energy use, mapping business activity, or exploring data transfer, these charts offer a powerful method for conveying information in a clear, logical manner. With the right tools and strategic planning, Sankey diagrams can be an invaluable component of any data visualization strategy.

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