Visualizing Flow: The Art of Sankey Charts

Sankey diagrams, named after Marko D. Vanek (later known as Willi Sankey), a British chemist and manager of the steam plant at the National Physical Laboratory, are a powerful tool for visualizing the flow, distribution, and transformation of quantities. These charts, used as flow diagrams, have been particularly popular in the visualization of energy use, environmental, and economic processes, including supply chains, money flow, and data processing flows. Sankey charts use arrows that are both labeled and unequally spaced. The width of these arrows is proportional to the flow rate (or probability), creating a visual map of quantity. This unique blend of clarity and dynamism makes Sankey Diagrams a potent data visualization tool in a variety of contexts.

Crafting a Sankey Chart

Creating a Sankey chart involves several steps. The first step is defining the flow process. This involves identifying the starting and ending points of the flow and the stages in between. Once the process is clearly defined, the flow rates or amounts need to be assigned. This step is crucial for determining the width of the arrows.

The next step is to organize the data on the chart. Sankey diagrams typically show the inputs for a system on the left side and outputs on the right side. The intermediate processes or phases are arranged in between. Each stage can be labeled with a category, subcategory, or specific process name to facilitate easier understanding.

Once the structure is set, the next concern is to map the flow rates. The width of the arrows is determined by the proportional value of the flow rates. For example, a high flow rate could result in a wide arrow, visually reinforcing the quantitative value of the flow. The legend play a key role in translating these visual cues to numerical data for users.

Applications of Sankey Charts

The applications of Sankey diagrams are varied and profound. It’s crucial to understand the nature of the process or flow being visualized to choose the right kind of Sankey chart. Here are some applications and examples:

*Energy Transformation and Consumption: *Sankey diagrams are often used to show the flow of energy from a source, through various stages of conversion or loss, and finally to the end use. For example, a comprehensive Sankey chart can illustrate how much energy is lost as heat or converted into electricity as the energy from a renewable source passes through various stages to eventually reach a home.

*Supply Chain Analysis: *These diagrams can also be used to provide a detailed view of a supply chain. By visually mapping raw materials entering a supply chain to the finished products leaving it, Sankey charts can highlight potential bottlenecks, inefficiencies, or points of interest for improvement.

*Causal Analysis: *In the field of statistics and marketing, Sankey diagrams can be used to visualize the causal pathways linking different factors or variables. For instance, in digital marketing, they can show how various marketing channels influence customer purchase decisions or engagement.

*Economic Transfers: *Sankey diagrams are also excellent tools for visualizing the flow of economic transfers, such as money or resources, between different entities or levels. This is particularly useful in understanding the structure and efficiency of programs, projects, or investments.

Best Practices and Tips

To ensure clarity and effectiveness, it’s important to apply best practices in creating and interpreting Sankey diagrams. Here are some tips:

1. Label Clearly: Ensure that all inputs, outputs, and intermediate stages are clearly labeled with units and values.
2. Simplicity is Key: Overcrowding of data can confuse rather than clarify. Use clear and concise labeling.
3. Legend Unambiguous: The legend should be easy to understand and should accurately represent the data.
4. Be Consistent: Use a consistent scale and color scheme to ensure that the chart is both legible and pleasing to the eye.

Sankey charts are a versatile tool for visualizing flow and transformation processes. Whether in understanding complex energy flows, evaluating supply chain efficiency, or analyzing economic transfers, these charts offer a dynamic and intuitive way to represent vast amounts of data. By employing these charts effectively, data visualization professionals can communicate complex information in a compelling and insightful manner.

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