Visualizing Flows with Sankey: Unveiling Data Stories in a Stream of Charts

In the realm of data visualization, the Sankey chart stands out as a powerful tool for illustrating complex data interactions and flows in a visually engaging manner. This type of chart is named after Maurice Wilkes, an English computer scientist, who invented the device, but it was Thomas J. Watson, Jr., of International Business Machines (IBM), who patented it and widely popularized its use in the 1960s for energy flows in nuclear reactors. Today, Sankey diagrams are used across various industries and fields to represent data flows, energy use, ecological footprints, economic transactions, and much more. In this article, we’ll explore the creation of Sankey diagrams and their myriad applications, uncovering the stories hidden within data flows.

Understanding the Basics of Sankey Charts

A Sankey diagram is a type of flow diagram that represents the quantity of items flowing between steps in a process. These diagrams are particularly useful for showing how resources are transferred from an input to an output along multiple steps in different amounts. The most common feature of a Sankey chart is the use of colored lines, which visually represent the flow of items. The width of these lines is directly proportional to the amount of items flowing through each step. This allows viewers to quickly understand patterns and percentages involved in the flow process.

Creating a Sankey Chart: Step-by-Step Guide

Creating a Sankey chart involves data preparation and visualization in a systematic manner. Here’s a step-by-step guide to help you visualize your own data using Sankey diagrams:

1. Collect and Prepare Your Data: Ensure your data is organized clearly, with categories of input and output labeled precisely. The data often includes numeric values that represent the quantity of flow at each step.

2. Assign Positions: Decide on the order of the categories on the chart. Usually, the process flow is from left to right, with inputs on the left and outputs on the right.

3. Determine Width Ratios: Calculate the width of each line using the formula: (amount of flow at each step / maximum amount of any step) * width of the diagram. This will ensure that the widest lines represent the steps with the highest flow.

4. Choose Your Visualization Tools: There are many tools and software programs available that can help you create Sankey diagrams. Popular options include Tableau, Python’s matplotlib, and R’s sankeyNetwork or ggalluvial.

5. Create Your Sankey Diagram: Import your data into the chosen tool, and use the software’s features to draw the lines and labels. Some tools offer customization options for colors, line thickness, and textual descriptions, which can make your diagram visually appealing and informative.

6. Feedback and Iteration: Review the Sankey diagram for clarity and visual appeal. If necessary, adjust the data representation or stylistic choices to better tell your story.

Applications of Sankey Diagrams

Sankey diagrams are versatile tools, and their applicability spans across various fields. Here are a few notable applications:

• Energy Analysis: They are commonly used to analyze the energy balance of processes, showing how energy is generated, transformed, and consumed.

• Economic Transactions: Sankey diagrams can illustrate the flow of goods and services within an economy, helping to understand trade relations.

• Financial Flows: In finance, these diagrams are used to visualize the movement of funds in an investment portfolio or a company’s financial statements.

• Healthcare Outcomes: Sankey diagrams can be used to demonstrate the progression of patients through healthcare processes, highlighting potential bottlenecks or inefficiencies.

• Project or Process Flows: In project management, they are used to track the progress of projects, showing how tasks are related and influencing one another.

Conclusion

Sankey diagrams are a powerful visualization tool that can help uncover the stories within data flows. Their ability to represent complex flows in a simple, intuitive way makes them an invaluable resource for data analysts, scientists, educators, and business professionals. With the right data organization, visualization tools, and attention to aesthetic details, Sankey diagrams can transform the way we understand and interpret datasets, making the often intricate details of information flows accessible to anyone.

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