Flow Visualized: The Art of the Sankey Chart

Sankey diagrams are a type of flow diagram often used to visualize the quantities of materials, energy, or cost moving through a process system, by showing the quantity of flow. First introduced by English physicist and engineer William Playfair in the 19th century, Sankey diagrams have remained popular due to their ability to convey the flow and energy transfer in complex systems at a glance. This article delves into the art and science of creating Sankey diagrams, their diverse applications, and the nuanced understanding they provide of system dynamics.

The Craft of Creation

Creating a Sankey chart involves a systematic approach to data visualization that requires careful planning and design:

1. Data Collection: The process starts with the collection of data that needs to be visualized. This could be an analysis of energy flows, material conversion rates, financial budgets, or the flow of customers through a business process.

2. Process Mapping: Understanding the process that the Sankey diagram is meant to represent is crucial. You need to map out all the components and the quantities of flow involved between them.

3. Determining Flow Quantities: For each component in the process, you must establish a consistent unit of flow, such as money spent per month, kilowatt-hours of energy consumed per hour, or kg of material processed per day.

4. Sankey Chart Structure: The diagram has a set of horizontal lines (or Sankey arrows) along which the flow is displayed. Larger arrows indicate higher quantities of flow.

5. Connecting Components: Components are linked by arrows, which should be wide and thin enough to clearly represent the intensity of the flow between them. Branches from a larger arrow are typically longer if the flow into that branch is higher.

6. Calibrating the Diagram: A balance between the size of the elements and the arrows must be achieved. The aim is to ensure that the reader can understand the relative magnitude of flow between different components.

7. Incorporating Units: Units of measurement for the flow should be clearly legible and integrated within the diagram without cluttering the visual flow.

8. Labeling: Providing labels for each component helps in understanding the diagram’s specifics and can improve its readability.

The Artistic Aspect

Creating a Sankey diagram is as much an artistic endeavor as it is a scientific one. Artists must consider the following to ensure their diagram not only represents data effectively but also has an aesthetically pleasing presentation:

1. Aesthetic Consistency: Use of color schemes, fonts, and line styles should be consistent to maintain a visually cohesive diagram.

2. Legibility: The chart should be easy to read and interpret. Elements that are too small or that lack clear contrast will confuse the reader.

3. Balance: The spacing, scale, and arrangement of lines should feel balanced. The eye can follow the flow through the diagram without unnecessary interruptions.

4. Focus: It’s important to highlight the most significant flows with more obvious line thicknesses to draw attention to key areas of interest.

Applications

Sankey diagrams are particularly useful in the following areas:

1. Engineering: In energy systems, they help illustrate the efficiency of power generation and the energy flow through a power plant or transmission system.

2. Environmental Science: Sankey diagrams are employed to visualize carbon footprints, resource consumption, and water cycles.

3. Finance and Economics: They provide insights into the distribution of funds across different sectors or the flow of cash in financial systems.

4. Supply Chain Management: Sankey diagrams can illustrate product flows through the supply chain, highlighting inefficiencies or bottlenecks.

5. Business Operations: They help visualize customer flows through a company, project finance streams, and other operational processes.

6. Research and Innovation: Sankey diagrams can streamline complex multi-dimensional datasets, helping researchers understand complex processes better.

Sankey charts offer a powerful yet nuanced tool for visualizing the complex systems we interact with daily. With proper creation and artistic considerations, these diagrams can communicate vast amounts of information in a compact, visually engaging, and intuitive manner. The art of the Sankey chart lies in its ability to balance clarity, detail, and the aesthetic principles necessary to transform a blob of data into a clear picture of system dynamics.

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