Mastering the Sankey Chart: Understanding the Art of Visualizing Flow and Distribution Using Sankey Diagrams
Sankey Charts, named after William John Macquorn Rankine, an influential early 19th-century Scottish engineer and physicist, have become invaluable tools across diverse professional fields like energy management, supply chain and logistics, economics, environmental studies, and much more. These visual representations utilize a unique diagrammatic approach to elucidate the flow, distribution, and transformation of entities like energy, material, services, money, or information from one place to another. Mastering the art of creating effective Sankey diagrams requires not just a grasp of the design principles but an understanding of the intricacies involved in their use within the chosen domain.
### What is a Sankey Chart?
At its core, a Sankey diagram is a graphical depiction of flow that shows the movement of quantities from one part of a system to another in the relative sizes based on their volumes, pressures, or currents. It utilizes arrows or bands whose widths are proportional to the quantity of the flow they represent, providing a visually intuitive method that can quickly communicate complex information flows and the dynamics of inter-regional exchanges.
### Key Components of a Sankey Diagram
**Nodes**: Typically depicted as rectangles, circles, or polygons, these represent starting points, end points, or intermediate nodes of a system. They might represent data or information points, sources of materials or energy, or destinations in a supply chain.
**Links or Bands**: These connect the nodes and represent the flow between them. The width of the bands is proportional to the value they represent, visually emphasizing the magnitude of flow from the source node to the destination node.
**Flow Values**: These values are usually annotated on the Sankey diagram to provide concrete data about the flow quantities. This could be anything from energy output per region, material throughput in a supply chain, monetary transactions between different economic areas, etc.
### Creating Effective Sankey Diagrams
1. **Define the Purpose**: Before creating a Sankey diagram, it’s essential to clarify what the intended viewers should get out of the data. This will dictate the flow values and the categories of data points, helping to shape the design.
2. **Collect Data**: Gather accurate data on the flows you wish to represent. Ensure the dataset includes flow quantities, node identifiers, and directions of flow. This data will directly inform the values, arrows’ widths, and the connectivity of nodes in your Sankey diagram.
3. **Choose Appropriate Software Tools**: There are numerous software options for creating effective Sankey diagrams, such as Tableau, Microsoft Power BI, Gephi, and specialized tools like SankeyMapper.com. Select a tool that aligns with your proficiency level and the software’s feature set that best meets your specific needs.
4. **Design the Layout**: Arrange your nodes based on appropriate categories or for a clearer visual impact. Decide on a meaningful layout that keeps the diagram tidy and logical, often starting with a designated ‘source’ node and proceeding through the system to the ‘sink’.
5. **Annotate with Key Data**: Clearly label your nodes and edges to convey the most important facts associated with the flows. This could include flow values, node names, and flow directions.
6. **Aid Perception**: Utilize colors to distinguish between different nodes or flow types effectively. This helps in comparing the volume of flows and understanding the relationships between different parts of the system.
### Example Application
Imagine illustrating the global energy distribution across different forms such as coal, oil, gas, renewables, and nuclear. A Sankey diagram could depict how total energy production (nodes) is channeled into final energy use (another node category), illustrating energy transformation steps (flow lines of variable widths corresponding to consumption or production volumes). Visual distinctions for each energy type could aid easily in distinguishing volumes and highlighting major energy flow patterns.
### Conclusion
Mastering the creation and interpretation of Sankey diagrams is foundational for professionals requiring a sophisticated approach to represent flow dynamics in various sectors. By understanding how to design effective Sankey diagrams, incorporating a well-chosen set of nodes, thoughtful use of flow value representation, and clear labeling, one can effectively communicate complex data flows, driving informed decision-making and strategic insights. Whether the application is in assessing energy efficiency in buildings, optimizing supply chain logistics, or visualizing the circulation of funds in financial systems, the art of creating illustrative Sankey diagrams opens the door to a nuanced and powerful analytical tool in data visualization.
