Flowing Funnels: Unraveling the Story of Sankey Charts

In the world of data visualization, the Sankey chart stands as an unparalleled marvel, capable of illustrating the flow of energy, materials, and finance within any given system with remarkable clarity. Despite its somewhat obtuse name, Sankey chart creation showcases both creativity and technical finesse, making it a favored choice among data scientists, systems analysts, and decision-makers across various industries. Let’s delve deeper into the story of Sankey charts, their creation process, and their myriad applications.

Sankey Charts: A Brief History

Sankey diagrams trace their origin back through the centuries to the early 19th century. They are named after an English engineer, William Playfair, who is also credited with the creation of the bar chart and line graph. Playfair was the first to use diagrams to depict the distribution and movement of coal and steam energy. However, it was not until more than a century later that these diagrams became known as ‘Sankey diagrams’ after a British engineer named Dr. Michael Sankey, who developed them for the engineering firm of Thomas Edison in the early 20th century.

The Anatomy of a Sankey Chart

Sankey charts have a distinctive, flow-like shape, with arrows that indicate the movement of energy or materials. Below are the primary components of a Sankey chart:

• Flow Channels: These are the primary vertical or horizontal pathways along which energy, materials, or finance are moved.
• Arrows: Represent the flow rate between channels, with the width of the arrows indicating the magnitude of the flow.
• Sources and Sinks: These are the points where flows enter (sources) or leave (sinks) the system being described.
• Nodes: The smallest points or boxes that the channels divide into, representing components or processes between the source and the sink.
• Labels: Added to both channels and nodes, labels provide additional context or details about the data represented.

Creating Sankey Charts

Creating a Sankey chart involves several steps:

1. Data Acquisition: Gather the data that you want to visualize. This could include energy consumption, goods movement, or funding allocation.
2. Flow Determination: Decide which variables to represent as flows and which as nodes or stations. Choose a flow width scale.
3. Constructing Channels: Make horizontal or vertical channels to represent flows within the system.
4. Drawing Arrows: Place arrows between nodes, ensuring that the width of the arrow is proportional to the flow quantity.
5. Incorporating Labels and Sources/Sinks: Add labels to nodes and channels to provide context and identify points of entry and exit in the system.
6. Adjustment: Fine-tune the chart by adjusting the sizes of nodes, the width of the arrows, and the orientation of the channels.

Many data analysis tools, such as R, Python’s Matplotlib, and dedicated software like Sankey.js, support the creation of Sankey charts.

Applications of Sankey Charts

Sankey charts are particularly useful when visualizing complex processes involving numerous variables, as they help in identifying major inefficiencies and bottlenecks. Here are some typical applications:

• Energy Systems: They are used to illustrate efficiency in energy production, distribution, and consumption.
• Materials Flow: For visualizing the flow of raw materials through a manufacturing process to analyze recycling rates and waste streams.
• Economic Analysis: Tracking the flow of funds in a business or a portfolio during a certain timeframe.
• Environmental Science: Showcasing carbon emissions, water usage, or waste generation across different sectors.
• Healthcare Logistics: Illustrating the patient flow through a medical system or the distribution of healthcare resources.
• Supply Chain Management: Mapping the flow of goods from procurement to distribution to end-consumption, highlighting opportunities for optimizations.

Conclusion

Sankey charts have evolved from a 19th-century invention to a modern tool of data visualization, providing an elegant way to depict complex processes. Their ability to convey large and intricate datasets in an easily comprehensible manner is unmatched. Whether you are an engineer auditing an energy system, a financial analyst, or an environmental scientist, Sankey charts offer valuable insights that can lead to improvements, policy changes, and enhanced decision-making across a vast array of sectors. As such, the story of Sankey charts is far from over; they continue to flow, shaping how we understand and interact with our interconnected world.

SankeyMaster

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