Flow Through: Illustrating Data Movement with Sankey Charts

Sankey charts have emerged as a powerful visual tool for illustrating data movement within complex systems. Unlike traditional bar graphs and line graphs that only present data points and trends, Sankey charts offer a holistic view of how information, resources, or data flow through a system. This article explores the creation of Sankey charts, the principles behind their design, and their diverse applications across various fields.

Understanding Sankey Charts

Sankey charts, named after Colonel Sankey, a British engineer who used them to visualize energy flow in steam engines, are structured diagrams that represent flows and transfers between multiple processes. Each flow is represented by a series of bars (or edges) that are assigned a width proportional to the flow rate. The width of the bars helps the reader visualize the relative importance or magnitude of each flow.

Creating Sankey Charts

Creating a Sankey chart involves several steps. First, identifying the sources, processes, and sinks (the final destinations) is crucial. These elements represent the beginning, the flow through processes, and the end points of the data or resources. Once these points are established, the next step is to quantify the flow rate for each component. This is where software comes into play. Many graphing software packages, including R and Python libraries (e.g., Matplotlib, Plotly, and Altair), offer Sankey diagrams as standard or through additional packages. These tools simplify the process of creating a Sankey diagram, allowing users to import data and generate the chart without extensive technical knowledge.

Parameters for Sankey Charts

Several parameters are crucial in designing an effective Sankey chart. The first is the number of flow steps, representing the number of processes or changes in the data. The second is the thickness of the flow, which is often proportional to the size of the flow. Adjusting the flow width can make small flows more visible against large flows, enhancing the readability of the chart. Additionally, the placement of nodes (the points where flows begin and end) can significantly affect the readability of the diagram. A good balance between tight, which minimizes space between nodes, and loose, which allows for better flow separation, is essential.

Applications of Sankey Charts

Sankey charts are versatile and have been used across a wide range of applications. In energy analysis, they are invaluable for visualizing energy flows and losses in buildings or power systems. In environmental science, they help to illustrate the flow of waste or pollutants through different environmental processes. Even in social sciences, Sankey charts can depict the movement of individuals through different job types or educational levels over time.

Case Study: Financial Flow

A compelling use of Sankey charts is in financial analysis. A recent study by a financial consulting firm used Sankey diagrams to illustrate the flow of investments through various assets, sectors, and over different periods. This was particularly useful for stakeholders who needed to see the distribution of their investments across different sectors, and how their portfolio flowed from one asset class to another over time.

Best Practices for Designing Sankey Charts

While making Sankey charts might seem straightforward once the data is quantified, there are several best practices to ensure the chart effectively communicates its intended message. Ensure the Sankey chart is visually balanced with equal and proportional spaces for each flow step. Use a clear, identifiable color scheme for your flows, avoiding the use of too many colors or gradients at the risk of making the chart too busy. Finally, legends explaining each flow or color should be clearly indicated.

Conclusion

Sankey charts are a valuable tool for illustrating complex data flows and processes. By effectively representing data movement through nodes and connected edges, they offer a clear and concise way to communicate intricate information. Whether analyzing energy consumption, understanding the flow of investments, or mapping the progression of information through a system, Sankey charts are a versatile and powerful visualization tool. As data-driven decision making becomes more prevalent, the role of Sankey charts in facilitating understanding and communication in complex data sets is bound to grow.

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