Sankey charts are a powerful data visualization tool that help to communicate complex flows and relationships between data points in a visually engaging way. Named after the Scottish engineer and inventor Matthew Henry Phineas Riall Sankey, who first used this type of chart to show energy usage in 1898, the Sankey chart has evolved over the years and is now an essential component of data visualization toolbox. In this article, we will explore how to create and apply Sankey charts to communicate data insights effectively.
Understanding Sankey Charts
Sankey charts represent flows or transfers between data points. The width of the arrows, also referred to as ‘band widths’, indicates the magnitude or importance of the flow. Typically, they use stacked rectangles to show the quantities or volumes of these flows. Sankey charts can be applied in various fields, such as economics, energy distribution, water networks, and processes in engineering to help users understand the relationships and movements of entities.
Key Components of Sankey Charts
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Sources: These are the starting points or origins of the flows. Sources are usually represented at the top or the beginning of the chart.
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Sinks: These are the destination points or terminations of flows. Sinks are shown at the bottom or the end of the Sankey diagram.
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Nodes: These are nodes where flows are combined or split. Nodes can be represented as blocks or symbols and are placed between sources and sinks.
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Flows: This refers to the actual data being visualized. Flows are the connections that run through the diagram, and their width represents the volume or magnitude of the flow.
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Labels: Text labels are used to provide context or identify the flows, sources, and sinks.
Creating a Sankey Chart
Step 1: Data Preparation
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Collect Data: Gather all the necessary data that you want to visualize, including sources, sinks, specific flows, and their volumes.
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Structure Data: Organize your data in a table format. Ensure your table includes columns for sources, sinks, the flow name, and the flow volume for each data set.
Step 2: Choose Software
- Select a Tool: Depending on your level of expertise and available resources, choose a tool to create your Sankey chart. Popular options include Microsoft Excel, Tableau, PowerBI, R (with packages like ggplot2 and ggraph), Python with libraries like matplotlib and networkx.
Step 3: Design the Chart
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Layout and Sizing: Arrange sources, nodes, and sinks with sufficient space to read the labels. Adjust the size of the chart to match the amount of data and audience size.
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Color Scheme: Use color to create a clear distinction between different flows, and also to add visual appeal and interest.
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Node and Arrow Styles: Customize node and arrow styles to ensure clarity and readability. This includes width, color, and shape adjustments.
Step 4: Verify Data Accuracy
Double-check the data you are plotting to ensure accuracy. Incorrect data can lead to misinterpretation of the flow patterns and relationships.
Step 5: Review and Feedback
- Initial Review: Examine the chart for any inconsistencies, logical errors, or aesthetic issues.
- Seek Feedback: If possible, gather feedback from peers or stakeholders to ensure the chart conveys the intended message effectively.
Applications of Sankey Charts
- Energy Distribution: Show how energy flows through a network, from sources to points of use.
- Economic Flows: Illustrate the movement of goods, services, or capital between countries or sectors.
- Traffic Flows: Display traffic patterns in road networks, identifying congestion areas or routes.
- Social Networks: Visualize connections or interactions among individuals or groups in online social platforms.
Conclusion
Sankey charts are an excellent tool for revealing the dynamics of flow in data-rich environments. They offer a clear visualization of data movement, making it easier to understand complex relationships and patterns. By following the steps outlined in designing a chart, you can effectively communicate your data’s story through a visually compelling, Sankey chart.
Ultimately, the art and science of creating Sankey charts lie in not just their aesthetics but their ability to help readers grasp the underlying structure and trends that data can often obscure. Understanding your data thoroughly and leveraging the right visualization tool helps in making informed decisions based on visual data insights.
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