Sankey Charts: Visualizing Flow and Relationships in Data

Sankey Charts are a type of flow diagram characterized by their distinctive thick lines that visualize the flow quantities in a process. Named after Irish Captain Matthew Henry Phineas Riall Sankey, who used this type of diagram in a 1898 publication on steam engine efficiency, Sankey Charts have since found applications across various fields. They are particularly valued for their ability to depict multiple flows and their quantities in relation to each other, highlighting how inputs are transformed into outputs through various stages.

What is a Sankey Chart?

A Sankey Chart is a visualization tool used to display a flow of data between different stages or entities. The width of the lines or arrows in the chart is proportional to the flow quantity they represent, making it easy to see where the most significant parts of the flow are concentrated. Sankey Charts can illustrate not only the quantity but also the efficiency, loss, or conservation within a system.

Interactive Sankey Chart Example

Try our interactive sankey chart example below!

Nodes (comma-separated, e.g., Source, Target): Source Indices (comma-separated, e.g., 0,0,1): Target Indices (comma-separated, e.g., 1,2,3): Values (comma-separated, e.g., 10,15,5):

Applications of Sankey Charts

Sankey Charts are versatile and can be applied in numerous areas, including:

Energy Efficiency: Showing the distribution of energy sources and their conversion into useful output or losses.
Supply Chain and Logistics: Visualizing the flow of materials, products, and costs through the various stages of supply chains.
Cost Breakdowns: Illustrating how total costs are distributed across different components or departments.
Traffic Flow: Mapping the movement of traffic through networks to identify high-volume paths and bottlenecks.

Benefits of Using Sankey Charts

Clear Visualization of Flows: Easily identify major and minor flows within the system, highlighting inefficiencies or key areas of interest.
Detailed Insight: By showing how different stages or components are connected, Sankey Charts provide insight into the relationships within the data.
Efficiency Analysis: Ideal for analyzing and presenting energy or material efficiencies and losses in a process.
Customization: Can be customized with colors and labels to enhance readability and convey additional information about the flows.

How to Interpret Sankey Charts

Interpreting a Sankey Chart involves understanding its structure and components:

Nodes: Represent stages, processes, or entities where the flow originates, passes through, or ends.
Links (Flows): The arrows or lines connecting nodes, with their width proportional to the flow quantity.
Direction: The flow direction, usually from left to right or top to bottom, indicating the progression or transformation of the flow.
Color Coding: May be used to represent different types of flows or to distinguish between various data streams.

Best Practices for Creating Effective Sankey Charts

Simplify: While Sankey Charts can handle complex data, it's essential to keep them as simple as possible for clarity.
Logical Layout: Arrange nodes in a way that makes the flow easy to follow, avoiding unnecessary crossings of links.
Consistent Scale: Ensure the width of the flows is consistent across the chart to accurately reflect quantities.
Use Colors Purposefully: Apply colors to differentiate between types of flows or to highlight particular paths or stages.

Conclusion

Sankey Charts are an excellent tool for visualizing complex flow data in a manner that is both informative and aesthetically pleasing. By providing a clear picture of how resources, energy, or information move through a system, they enable stakeholders to identify key areas for improvement, optimization, or further analysis. Whether used in environmental studies, finance, logistics, or any field involving flows and processes, Sankey Charts can turn intricate data into actionable insights.

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