Flow Visualization Unveiled: The Art and Insight of Sankey Charts

In the sprawling world of data visualization, the Sankey chart stands as a unique and powerful tool for illustrating the flow of energy, material, and information. A relative outlier in the pantheon of graphical representations, the Sankey chart harnesses the visual language of flow to reveal patterns and inefficiencies not immediately apparent in tabular or scatter plot formats. In this article, we will explore the creation and the applications of Sankey charts, highlighting their aesthetic qualities and their significance in modern data analysis.

The Genesis of the Sankey Chart

The Sankey chart was conceptualized in the latter half of the 19th century by Irish engineer Francis Ronaldson. However, it is the German engineer and engineer-economist MC Escher (Michael Kracht, his real name) who is widely credited with the modern form of the Sankey diagram in the 1920s. These diagrams have been named after him, and they are also known as Sankey plots or Sankey diagrams.

How Sankey Charts Work

A Sankey chart is essentially a directed flow diagram where an arrow is used to indicate direction along with the magnitude of the flow of something—energy, water, material, or money, for instance. Each Sankey diagram is designed with the following elements:

Pipes: Represent the flow and are the thickest where the flow is strongest and the thinnest where the flow is weakest.
Nodes: Are where two or more arrows meet, representing a change in flow.
Ports: Are symbols that appear on the outside of the diagram and represent sources or sinks which are where flow enters or leaves the system.
Labels and axes: Are applied to the chart to give it context and to help the audience understand the visualizations.

Crafting Sankey Charts: The Artistic Touch

The creation of Sankey charts is both an art and a science. Here are some key steps in the Sankey chart creation process:

Collecting Data: Initially, you must gather your data on the flows within your chosen system. This can be complex, as it requires understanding the intricacies of the data you want to visualize.
Defining Nodes and Links: You need to decide on the start and end points of your flow and how they are connected. Each link on the Sankey chart should correspond to a distinct flow or process.
Determining Vector Width: Sankey charts use the width of vectors to represent the data flow magnitude. For instance, if an arrow is 50 units wide, it may represent the flow of 50 units while a 10-unit wide arrow could represent a flow of 10 units.
Creating the Diagram: There are several software tools available for creating Sankey charts, such as Sankey Canvas, Tableau, Microsoft Excel, and Power BI. The process involves inputting the data, customizing the diagram, and ensuring that the visual elements are proportional to the data.
Review and Refine: Once the initial Sankey chart is created, it is important to review it for clarity, accuracy, and alignment with the goals of the data visualization.

Applications of Sankey Charts

Sankey charts are a versatile tool with a multitude of applications across various domains:

Energy Systems: Illustrating the energy flow in buildings, power plants, or the energy grid.
Material Flow Analysis: Tracking the flow of materials from extraction to production and disposal.
Financial Systems: Depicting how money moves within a company or throughout the economy.
Transportation Networks: Mapping out the movement of goods and people.

Insightful Qualities of Sankey Charts

Sankey charts allow for a number of unique insights into a system’s performance and efficiency:

Highlighting hotspots: You can quickly identify the processes or links that consume the most resources.
Revealing bottlenecks: By analyzing the thickness of the pipes, you can identify process inefficiencies.
Making comparisons: Sankey charts enable direct comparisons between systems and processes.

Conclusion

The Sankey chart, with its elegant flow patterns and clear visual representations, is a tool that can elevate the way we understand and analyze complex systems. Whether it’s in energy analysis or financial modeling, the Sankey chart offers a unique fusion of art and data science that allows us to see the unseen flows that shape our world. By embracing the challenge of creating a Sankey diagram, we unlock the potential to make more informed decisions, optimize processes, and reveal inefficiencies that could otherwise remain invisible. As we move towards more complex societies and systems, the Sankey chart is poised to play an increasingly vital role in the world of data visualization and analysis.

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