Flow Diagram Magic: Unveiling the Secrets of Sankey Charts

In the world of data visualization, Sankey charts have emerged as a powerful tool for illustrating the direction and magnitude of data flow between different entities. These charts, named after Mark B. Sankey, an engineer and mathematician, who applied them to the study of steam flows, have become essential for showing complex, multi-directional flows in a clear and easy-to-understand manner. However, understanding how to create and interpret Sankey charts can seem like a magical process to many. This article aims to unveil the secrets of creating and applying Sankey charts, thereby making this flow diagram magic accessible to all.

Understanding Sankey Charts

Sankey charts are a type of flow diagram that uses bars with widths proportional to the flow size and colored in a specific palette. These charts are most effective in displaying how something flows through different steps, systems, or stages. The primary use of Sankey diagrams is to visualize the distribution of data flow, such as energy flows within a system, financial transactions, or the flow of goods from production to consumption.

The Process of Creating a Sankey Chart

Creating a Sankey chart involves several steps, from data collection to visual presentation. While you can do this using basic Microsoft Excel, there are also numerous online tools and dedicated software that simplify the process. Below is a simplified guide on creating your own Sankey chart:

Step 1: Data Collection and Preparation

The first step involves collecting the data you intend to represent in your Sankey chart. This data should be in a format that can be arranged into a two-dimensional table, with the sources or inputs listed in the first column, and the sinks or outputs listed in the last column. The flow between sources and sinks should be recorded in the rows.

Step 2: Data Processing

Before you start drawing your chart, you need to normalize or scale your data. This means you make all your data points add up to 100% each. You do this by dividing each number by the total sum of all those numbers. This normalization is crucial for making the chart more meaningful and understandable.

Step 3: Calculating Flow Areas

After normalizing your data, the next step is calculating the flow areas. To do this, you multiply the normalized value by the width of your chart. This width is often set to a fixed value, such as 10 (for percentages). The idea is to scale your total values while keeping the scale consistent across all flows.

Step 4: Choosing a Tool

You can implement step 3 by hand with pen and paper, using a spreadsheet program, or by using more sophisticated software that automatically generates the chart based on your input data and other settings. There are several powerful tools that can help you create Sankey diagrams, such as Tableau, D3.js, Python’s matplotlib library, or even Google Sheets. Many of these tools use the data calculated in step 3 to generate the chart with the correct widths and coloring for each flow.

Step 5: Designing Your Sankey Chart

Once you’ve chosen the tool and filled in the input data, you’ll be ready to start designing your Sankey chart. This includes customizing the color scheme, font sizes, and other aspects to make the chart more visually appealing and easier to interpret.

Step 6: Feedback and Iteration

After you finish creating your Sankey chart, it’s beneficial to get feedback from other people. Their perspective can help you see aspects of the chart that may not be as clear as they should be, allowing you to iterate on your design and refine it.

Applications of Sankey Charts

Sankey charts are versatile tools used across various fields. In the energy sector, they are used to analyze energy flows within buildings, cities, or entire energy systems. In finance, they help in visualizing the flow of money through different accounts or investments. Additionally, they are invaluable in demonstrating consumer behavior, product distribution, and much more.

Conclusion

Sankey charts are a visual tool with the power to make complex flow data understandable and engaging. By understanding the process of creating them and knowing their applications, you can harness the “magic” of Sankey charts to communicate your data effectively. Whether you’re a data analyst, an educator, or just an enthusiast for visual storytelling, Sankey charts can be a valuable asset in your arsenal of data visualization techniques.

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