Flow charts, also known as Sankey diagrams, are a type of data visualization that allow you to represent the flow of elements between different points or categories in a clear and easy-to-understand way. These diagrams are particularly useful when you want to show the distribution, movement, or allocation of a particular quantity over time, or between different entities.
In this article, we’ll explore the concept and creation of compelling Sankey charts, highlighting some of the best practices and applications in various fields such as economics, environment, and urban planning.
Understanding Sankey Diagrams
What are Sankey Diagrams?
Sankey diagrams, named after Thomas Sankey, an engineer who used this type of graph in 1898 to depict industrial energy use, are a specialized form of flowchart that visually represents the quantity and direction of flow between connected nodes. Each flow is depicted with a width that corresponds to the volume of data it represents, making it easier to understand how resources or quantities are distributed across different categories or entities.
Types of Sankey Diagrams
Sankey diagrams can be categorized into two main types:
- Standard Sankey Diagram: This type features bars as the nodes and arrows for the flows, which are generally used for simpler data sets.
- Flowchart Sankey Diagram: Here, the nodes can take different shapes, such as rectangles or circles, making it suitable for more complex data structures.
Creating Compelling Sankey Charts
Data Preparation
Before creating your Sankey chart, you’ll need to prepare your data. You’ll typically work with three types of data:
- Source and Target Values: These represent the entities between which the flow is happening.
- Flows: The volume, amount, or quantity of the flow between each entity pair.
- Node Labels: Labels for each entity node.
Using Data Visualization Software
There are many software tools and platforms available for creating Sankey diagrams, including:
- MATLAB
- Python Matplotlib
- R library ‘networkD3’
- D3.js (JavaScript-based) for interactive charts
- Tableau
- Microsoft Power BI
Best Practices for Design
To create truly effective Sankey diagrams, it’s essential to adhere to several best practices:
- Choose the Right Software: Tailor your tools based on your project’s needs, your data’s complexity, and the audience’s technical expertise.
- Sort Nodes: Arrange the nodes in a way that makes sense for the narrative, such as sorting them by volume or value.
- Optimize Flow Widths: Ensure that the width of the flows visually corresponds to the magnitude of the data, making it easy to read at a glance.
- Use Color Strategically: Color the nodes and flows to highlight specific categories or trends, but avoid overly cluttered designs.
- Utilize Descriptive Node Labels: Make sure the labels for each node are clear and descriptive, aiding in understanding the context of the flows.
- Consider Interactive Elements: In interactive charts, consider adding features like tooltips, animated flows, and filters to enhance user engagement.
- Check for Clarity and Efficiency: Avoid clutter by removing unnecessary lines and nodes, and ensure that the chart is as efficient as possible.
Applications of Sankey Charts
Sankey diagrams find extensive use in a wide range of fields and applications:
- Energy Flow: Illustrating the generation, conversion, and distribution of energy.
- Material Flow Analysis: Showing the path and quantity of resources used or recycled in different sectors.
- Traffic Routing: Mapping the flow patterns across various road networks.
- Urban Planning: Depicting the movement of people, transport modes, or goods within a city.
Conclusion
Sankey charts, with their ability to visually illustrate the flow of quantities between entities, can provide valuable insights into complex data relationships. By following the design principles and best practices outlined in this article, you can create compelling Sankey diagrams that are not only informative but also engaging and easy to understand. Whether you’re analyzing energy use, tracking material flow, or mapping traffic patterns, Sankey diagrams offer a powerful tool for making your data more accessible and meaningful to your audience.
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