Flow Visualizations: The Art and Science Behind Sankey’s Secret Streams
Flow visualizations have been a silent yet powerful tool in the realm of analytics and system understanding for over a century. They offer a window into the unseen flows of energy, materials, and information, helping humans to visualize complex processes with remarkable clarity. Among these powerful visualization tools is the Sankey diagram, a type of flow diagram invented by Irish engineer William Playfair in 1845, later refined and renamed after German engineer Ernst Dietrich Philipp Sankey in the 1890s.
The Art of Creating Sankey Charts
Sankey diagrams, at first glance, are simple representations of systems, but they are quite complex to create. The process involves several steps:
1. Defining Process Boundaries
First, identify the boundaries of the process you wish to visualize. This will help determine the nodes or points of interest that represent inflows and outflows.
2. Selecting Variables and Measurements
Choose the variables to be represented—be it water flows, data, energy, or finance. Accuracy is critical, so measurements need to be as precise as possible.
3. Choosing a Scale
Sankey charts use different scales to represent flows, which are inherently variable. In essence, a thicker Sankey arrow conveys a more substantial flow.
4. Drawing Nodes and Arrows
Nodes are boxes that represent the processes, while the arrows indicate flow. The width of these arrows is proportional to the magnitude of flow they represent. However, for accurate comparisons, all arrows should align with the direction of flow.
5. Managing Convergence and Divergence
When arrows converge, the points of convergence should be as narrow as possible to reflect the decrease in flow, and when they diverge, they should widen as flow increases.
6. Ensuring Clarity
The diagram should be clear and easy to read, which often requires balancing detail and simplicity. This involves careful labeling and, if necessary, reducing the thickness of lines to avoid overcrowding.
The Science of Sankey Diagrams
Sankey diagrams are rooted in both physics and economics—a union that provides them with a broad range of applications. The science behind these diagrams lies in their ability to show the efficiency of processes by visually representing the flow of energy or material through a system.
1. Energy Efficiency
Sankey diagrams are particularly useful in depicting energy flows in complex systems. For instance, they can be used to illustrate how much energy is lost in conversion among different forms (e.g., heat lost in engines or transformers).
2. Financial and Technical Systems
In economic and technical systems, Sankey diagrams show financial or material flows, revealing where resources are being invested and where they are being wasted.
3. Transport and Logistics
In the transportation sector, Sankey diagrams can depict the route and cost of goods movement, providing insights into where efficiencies can be gained.
4. Environmental Studies
Environmentalists use Sankey diagrams to visualize how emissions, waste, and resources interact within ecosystems and how these cycles contribute to overall energy consumption and waste generation.
Sankey’s Legacy
Ernst Dietrich Philipp Sankey, whose name became synonymous with the diagrams, was a visionary who sought to combine the analytical with the illustrative. The Sankey diagram, unlike the pie chart or bar graph, has the unique ability to present both the scale of flows and their connections in a way that makes complex systems understandable.
Today, Sankey diagrams are widely used across various fields. They remain a vital tool in industrial analytics, energy auditing, environmental reporting, and complex system design. Their evolution, thanks to advances in computing and data analysis, continues to expand their capabilities.
Sankey diagrams, with their delicate balance of art and science, encapsulate the essence of flow visualizations as the silent architects of understanding, making the opaque transparent and the hidden visible. As we navigate the increasing complexity of modern systems, these visual treasures provide a crucial means for unraveling the intricacies of our world’s energy and material flows.
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