Flowing Ideas: How Sankey Charts Visualize the Path of Change

Sankey diagrams, named after Mark Sankey who used them to illustrate steam flow in engines, are a powerful tool for visualizing complex flows and transformations. These charts are particularly effective at depicting the path of change or transformation between sets of values, making them an invaluable resource in various fields such as environmental science, finance, data analytics, and more. In this article, we’ll explore how to create a Sankey chart and dive into its applications, illustrating with practical examples how Sankey diagrams visually represent change, flow, and transformation.

Understanding Sankey Charts

Sankey diagrams are a type of flow chart that visualizes how entities flow from one set to another, displaying these flows as parallel bars with width proportional to their quantity. They are particularly adept at showing changes in the proportions of flows. The chart is divided into several bars, each of which is segmented by junctions, which represent the final state of the flow.

Creating a Sankey Diagram

Creating a Sankey chart involves several steps and requires a good understanding of the data you wish to visualize. Below is a basic guide on how to go about it:

Gather your Data: This might include initial numbers, amounts, or proportions, and the flow or transformation rates.
Organize Data: Arrange your data in a tabular format with columns for the starting nodes, the transformation or movement, and the end nodes.
Calculate Flows: Adjust the proportions of the flows to ensure they represent your desired data and maintain visual clarity.
Determine Unit of Measurement: This will dictate how the widths of the bars are calculated.
Use Sankey Diagram Software: Several tools, both free and paid, can generate Sankey diagrams from your data. Software like Tableau, Python (with libraries such as matplotlib or plotly), and specific Sankey diagram generators can all be used.
Add Labels: Include clear labels for your starting nodes, transformations, and end nodes. These help to explain the chart to others.

Applications of Sankey Diagrams

Sankey diagrams are versatile and can be applied in a wide range of scenarios. Here are a few examples:

Economic Analysis: Evaluating the flow of resources between different sectors of the economy, such as energy production and consumption.
Environmental Science: Demonstrating the path that energy or materials take through different levels of use, waste, and recirculation.
Social Media Analytics: Visualizing how information spreads across platforms or how traffic flows through different social media groups.
Financial Models: Displaying the flow of investment, funding, or capital through different industries or between various investment vehicles.

Practical Example

Let’s consider a simple example of an energy transformation. Imagine we have an energy-consuming device that uses electricity. The initial energy inflow (the green input bar in the diagram) shows the total amount of electricity fed into the device. The red and blue branches represent the efficiency losses of converting electrical energy into useful energy and the wastage in the form of heat, respectively.

In this hypothetical scenario, the width of the green bar is much larger than that of the red and blue branches, showing a high overall efficiency. This visual depiction of the energy transformation process is far more intuitive than simple numbers, making Sankey charts a powerful tool for conveying complex processes in a clear and accessible manner.

Conclusion

Sankey diagrams are a rich and effective way to visualize and communicate complex processes. By illustrating the path of change or transformation between sets of values, they provide a clear and engaging way to understand the relationships between variables. Whether you’re an environmental scientist evaluating energy flows or a social media analyst tracking the spread of information, Sankey diagrams offer a powerful tool for translating data into insights that others can easily grasp.

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