Sankey charts, also known as flow charts, are a type of diagram that uses arrows or bands flowing between nodes to represent the direction and magnitude of flows. This guide provides an overview of what Sankey charts are, how they are used, and the steps to create and interpret these powerful visual tools, enabling effective visualization of data, energy, or any other type of flow.
**Understanding Sankey Charts**
Sankey charts were created by mathematicians Hermann Krause and Philip Charles Johnson Sankey in the 1890s. Often used by engineers and economists, these charts are particularly useful for representing resources, materials, energy transfers, and financial flows in a clear and precise visual format, revealing both quantities and proportions at a glance.
**Components of a Sankey Chart**
**Nodes**: The points or terminations in a Sankey diagram carry labels and represent entities such as factories, sources, or regions. These nodes define the beginning and end of flows.
**Arrows/Bands (Links)**: These represent the quantities of flow between nodes. The width of the arrow reflects the amount of material, energy, or resources flowing in one direction, emphasizing the value of the flow.
**Angles and Dips**: These visuals indicate the changing direction of flow. As the bands get narrower or wider, the viewer can quickly deduce where more significant quantities are moving or accumulating.
**Interpreting Sankey Charts**
To effectively interpret a Sankey chart, begin by surveying the overall flow pattern, noticing if certain nodes are receiving more or fewer flows than others. This can help identify key sources, sinks, and pathways of flow. Next, analyze the thickness and length of the bands to gauge the volume of the flow and its direction. By following the direction of the bands, you can trace the path of the flow through the nodes.
**Creating a Sankey Chart**
**Step 1**: Collect and Organize Your Data
Gather all relevant data about the flow you wish to visualize, including the source nodes, destination nodes, and the quantities of flows between them. Categorize this information to ensure that it can be easily translated into the required visual components of a Sankey diagram.
**Step 2**: Choose Your Tools
While many software options exist, it’s important to select one that supports creating Sankey charts effectively. Options like Tableau, Microsoft Power BI, D3.js (for custom HTML chart creation), and visualization libraries such as Plotly or yEd Graph Editor may be suitable.
**Step 3**: Input Your Data
Using your chosen tool, input the data collected in the previous step. Most data visualization software includes functionalities that allow specifying nodes and links, quantities, and labels, streamlining the creation of the chart.
**Step 4**: Adjust Layout
Adjust the layout of the chart to optimize readability and visual clarity. Pay attention to the widths of the bands, their positioning on the graph, and the labels used. Utilize features within the tool’s interface for adjustments, such as sorting the nodes, adjusting arrow lengths, and fine-tuning band widths to represent the volume of flows accurately.
**Step 5**: Add Customization and Final Touches
Incorporate colors, transparency, and size variations to different bands for added clarity. This can help draw attention to significant flows and enhance overall comprehension.
**Step 6**: Review and Revise
Examine the final chart carefully to ensure that all aspects accurately convey the intended flow and that no critical information is obscured. Ensure that the labels are clear and that the chart provides a complete story without leaving the viewer with questions.
**Step 7**: Present and Share
Once your Sankey chart is complete, it’s time to make it accessible to your desired audience. This could be through a presentation, report, digital presentation, or print material. Make sure the chart is understandable and offers added value to the project or analysis you’re aiming to support.
**Conclusion**
Sankey charts are an indispensable tool for anyone needing to visualize and analyze data flows, whether in terms of material flow analysis (MFA), environmental studies, economic analysis, or general data set comparisons. By following the steps outlined in this guide, from understanding the basics through to mastering their creation and interpretation, you can leverage Sankey charts to communicate complex information with precision and clarity. Whether you’re a data analyst, student, or professional, the skills provided here empower you to use Sankey charts as an effective means to highlight and facilitate the understanding of various types of flow through your data.
