Sankey diagrams, a type of flow chart often used in the visualization of flows from one process to another, have significantly grown in popularity and utility over the years. They are especially valuable in fields such as environmental science, engineering, and energy data analysis. This article delves into the art and science of creating Sankey charts, highlighting the principles behind their design and the applications for which they are most effective.
The Science of Sankey Charts
Sankey diagrams are named after William Sankey, an architect and surveyor from England, who first used them in the late 19th century to visualize energy flow in steam engines. Today, these charts have evolved into powerful tools for data visualization, enabling the visualization of multi-step processes in a clear and effective manner. Here are some principles that guide the science behind Sankey diagrams:
1. Node Representation: Each step in a process is represented by a node. The nodes are connected by arrows, with the width of the arrow proportional to the amount of flow (energy, material, data) involved in that step.
2. Flow Continuity: Sankey diagrams ensure that any flow entering a given node must leave that node. This principle is crucial for accuracy and validity, ensuring a seamless flow of information from one step to another.
3. Solid Arrows: Using solid arrows to represent the flow is preferred over dotted lines, as it provides a clearer visualization of the process and its associated quantities.
4. Color Coding: It’s common to color-code nodes and arrows according to their category or type. This helps in easily distinguishing between different types of inputs, outputs, or transformations within a process.
5. Data Precision: The science of Sankey diagrams also involves careful consideration of data precision. It’s crucial to use the right units and scale for the data being represented, ensuring that the chart is both accurate and informative.
The Art of Sankey Chart Creation
While the science provides the foundational principles, the art lies in effectively communicating through visual design. Here are some artistic considerations for creating effective Sankey charts:
1. Chart Complexity: Sankey diagrams are capable of representing complex processes but can easily become too crowded if not properly designed. It’s essential to balance complexity with clarity and simplicity.
2. Legibility: The text labels should be large enough to be read with ease, especially when the chart is displayed in a public setting or used in presentations. Font size, color, and positioning play crucial roles in achieving legibility.
3. Orientation: Sometimes, a vertical layout can be more effective for showing step-by-step processes, while a horizontal layout is better for parallel processes. The choice depends on the process being represented and the insights the creator aims to highlight.
4. Interactivity: While traditional Sankey diagrams rely on static visualization, modern tools offer the option for interactive Sankey diagrams that highlight processes on mouseover. This can enhance user engagement and data interpretation.
Applications and Examples
Sankey diagrams are used across a variety of domains, including energy flow analysis, financial flows, and data processing pipelines in the field of computer science. One of the most notable applications is in the visualization of energy consumption and waste in buildings, which helps in identifying inefficiencies and reducing energy usage. Another significant area of application is in supply chain analysis, where they can visualize how materials move through a process or system, highlighting waste or inefficiency points.
Conclusion
Visualizing flows with Sankey charts is an art and science that deserves attention and respect. By understanding both the principles of creation and the nuances of design, users can create Sankey diagrams that are not only informative but also engaging and meaningful to their audience. Whether in energy efficiency studies, supply chain optimization, or any field where flow processes are a critical aspect of analysis, the power of Sankey diagrams as a data visualization tool cannot be overstated.
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