Sankey diagrams, named after Charles S. Sankey, an Irish-born engineer, were first proposed in 1898. Now, these visualizations are highly sought after for illustrating data movement and connections, making them particularly useful in fields such as energy, environmental studies, and economics. This article delves into the creation of Sankey charts, how they work, and their widespread applications.

Understanding Sankey Diagrams

Sankey diagrams are a type of flow diagram that displays quantitative data using the lengths of arcs (for circular connections) or lengths of arrows (in general flow diagrams) to represent the varying magnitudes of the data being depicted. Their primary strength lies in showing how something flows from one process or system to another, making them a highly efficient tool for data visualization.

How Sankey Diagrams Work

To understand how Sankey diagrams work, imagine a typical household energy consumption flow chart. The primary source of energy (like electricity from the power company) flows into the household. However, not all energy is used efficiently; some is lost, and some is converted into useful power. The Sankey diagram would visually represent the percentages of this energy flow through different appliances or processes within the home.

In a general sense, a Sankey diagram usually consists of:

• Nodes: Represent the inputs and outputs to/from the process or system being depicted.
• Edges: Represent the flow of a quantity (like resources, energy, or information) between the nodes. The width (or length) of these edges is directly proportional to the quantity’s amount flowing through them.

Creating Sankey Diagrams

Creating a Sankey diagram can be done with a variety of tools, from simple spreadsheet software to advanced data visualization platforms. Here’s a step-by-step explanation for creating one using Microsoft Excel:

1. Data Preparation: Gather all the data that your Sankey diagram will need. You’ll typically need a starting point, a series of intermediary steps, and an ending point. You’ll also need to know the quantities associated with each step.

2. Structure: Organize your information in columns (or rows). You’ll need to calculate percentages for each process if you’re not given them.

3. Excel Setup: Use Excel’s “Insert” menu to create a basic chart. This should be a bar graph with the processes as your horizontal axis and the quantities as your vertical axis.

4. Sankey Chart: Use Excel’s “Add Chart Element” > “More Layout Items” to add text boxes for your labels. Then, manually adjust the width of the bar graph to match your percentages.

5. Finishing Touches: Use Excel’s “Format Data Series” to adjust the width and color of your bars to resemble an actual Sankey diagram.

Applications of Sankey Diagrams

Sankey diagrams are incredibly versatile in their application. They can be used to:

• Evaluate and compare the efficiency of different processes or the distribution of resources.
• Analyze and interpret data on environmental flows—such as energy loss or emissions.
• Assess the flow of information or data within a system.
• Understand the dynamics of financial flows in various sectors or economies.

Conclusion

Sankey diagrams offer a powerful and versatile tool for visualizing data flows and connections. Their ability to depict complex systems in an intuitive and easy-to-understand manner can aid decision-making and analysis across various fields. Whether you’re a researcher looking to explore energy efficiency or an economist analyzing financial flows, a Sankey diagram can be a valuable addition to your data visualization toolkit.

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