Sankey diagrams, named after Sankey, an Irish engineer who used them to visualize energy flows in steam engines, have evolved into a versatile tool for visualizing flows and transfers within complex systems. In today’s data-driven world, these charts are increasingly used for creative storytelling, making them a powerful instrument in the arsenal of data visualization. This article explores the creation of Sankey diagrams, their applications, and the creative possibilities they open up for visual storytelling.
Understanding Sankey Diagrams
A Sankey diagram is a specific type of flowmap that visually represents flow processes between different steps or categories. The key elements of a Sankey diagram include:
- Sources and Destinations: These are input and output categories from/to which/which the flows originate and terminate. This could be anything from energy sources to end-use, data sources to destinations, or various stages of a process.
- Flows: The actual movement of something (such as energy, water, data, etc.) between sources and destinations. These are represented by the length and thickness of the lines, with the width or size of the flows indicating the magnitude of the flow.
Creating a Sankey Diagram
Step 1: Define Your Flows
Start by identifying the sources, destinations, and the magnitude of the flows between them. This involves setting clear boundaries of your system and understanding the inputs and outputs.
Step 2: Data Collection and Preparation
Collect the relevant data. This could involve processes to measure or estimate flows between different categories. The data is then transformed into a table with the source, destination, and the magnitude of the flow. Each row should contain one flow.
Step 3: Choose Your Tool
There are several tools and libraries available for creating Sankey diagrams, including R’s ggplot2, Python’s plotly, Excel, and specialized software like Tableau. Choose a tool that aligns with your analytical needs and data visualization goals.
Step 4: Draw the Sankey
- Source and Destination Layout: Arrange the sources and destinations in a manner that visually interprets your data well. This could be a hierarchical layout or a force-directed algorithm layout.
- Flow Lines: Use the width and color of the flow lines to represent the magnitude of the flow. Ensure the diagram is legible and interpretable by keeping the number of flows manageable and using appropriate colors and thicknesses.
Applications of Sankey Diagrams
Sankey diagrams are highly versatile and can be applied in many domains for a wide range of purposes:
- Energy Flows: Evaluate energy efficiency and consumption in facilities and entire power systems.
- Information Flow: Analyze data flows within or between systems, such as data pipelines in information technology.
- Finance and Economics: Visualize budget allocations, financial flows, and economic interdependencies.
- Water Flows: Analyze water usage and distribution systems.
- Project Management: Demonstrate the flow of tasks or resources in project management.
Creative Storytelling with Sankey Diagrams
Sankey diagrams can be more than just informative; they can tell engaging stories. Consider the following storytelling strategies when creating your Sankey diagram:
- Emphasize Storytelling Elements: Focus on the narrative or theme of your data. For example, with a historical energy transition dataset, highlight key inflection points in energy sources.
- Incorporate Color and Design: Use color and design elements to guide viewer’s attention. For instance, significant or surprising flows could be highlighted with brighter colors or larger widths.
- Interactivity: In interactive applications, allow viewers to inspect details by hovering over or clicking on individual flows, enhancing the story’s accessibility.
Conclusion
Sankey diagrams are a powerful tool for visual storytelling, enabling users to interpret complex flows and transfers in a clear and engaging manner. By carefully defining flows, selecting the right tool, guiding the visual design, and telling a compelling story, one can leverage the full potential of Sankey diagrams to communicate data-driven narratives effectively. Whether for internal analysis, educational purposes, or public engagement, Sankey diagrams offer a unique blend of data visualization and storytelling, making them a valuable asset in the visualization toolkit.
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