Flowchart Elegance: Unveiling Insights with Sankey Charts

In the world of data visualization, the quest to represent complex data flows, energy transfers, or the volume of goods and services is both an art and a science. Among the various tools that data analysts, engineers, and researchers use to visualize these intricate relationships is the Sankey chart. This diagram type may not be as well-known as some, like the bar or line chart, but its powerful visual display makes it invaluable for revealing insights that would otherwise remain invisible. This article delves into the creation and application of Sankey charts, showing how flowchart elegance can transform data into a story that is both engaging and actionable.

Understanding the Sankey Diagram

At its core, a Sankey or flow diagram is a variant of the flowchart that uses arrows to represent the magnitude of flow in a process. It was developed by Irish engineer Matthew Sankey in the 19th century for the analysis of steam engines, which is why it’s named after him. Since then, its applications have expanded across numerous industries, providing a unique way to visualize information flows, energy transfers, and material transport.

Key Features of a Sankey Chart

Flow Direction: Sankey charts typically have a single direction of flow, typically from left to right, from the input to the output of the process.
Stream Width: The width of the arrows in a Sankey chart is proportional to the amount of flow of data or energy; this design concept ensures that the chart is readable even when dealing with huge variations in flow magnitude.
Efficiency: Arrows are drawn in such a way that they form compact loops with minimal intersection to illustrate the most efficient path for flow.
Sub-streams: To illustrate detail and complexity, Sankey diagrams can include sub-streams from the main flow, depicting the various routes of the process.

Creating Sankey Charts

Creating Sankey charts doesn’t require any specialized software, though many tools can help with the intricate design. The basic steps for constructing a Sankey chart are as follows:

Define the Purpose and Data: Begin by understanding why you’re creating the Sankey chart and what data you’ll be using. Are you visualizing an energy flow, data movement, or water usage?
Decide on the Process Steps: Break down the process you wish to illustrate into its constituent steps. Determine the starting source and the final outcome, as these will form the endpoints of your Sankey diagram.
Estimate Flow Quantities: Gather the specific data you need in numerical form. These flow quantities will be proportional to the widths of the arrows in your Sankey diagram.
Choose a Sankey Chart Tool: For users without expert drawing skills, software tools such as Microsoft Excel (using a VBA script or add-ins), Tableau, Microsoft Visio, or specialized Sankey diagramming tools like Sankey Diagrammer or SankeyEditor can be extremely helpful.
Construct the Diagram: Using your chosen tool, input your process steps, data, and flow quantities. Begin drawing the arrows, following the guidelines of a Sankey chart to ensure they adhere to width and flow efficiency.
Review and Iterate: Once the initial diagram is complete, take the time to review it for readability and clarity. Adjust the widths of the arrows, labels, and angles of the streams as needed to enhance understanding.

Applications of Sankey Charts

The versatility and effectiveness of Sankey diagrams have seen them applied in a variety of fields:

Energy and Environmental Studies

Sankey diagrams are especially useful in measuring and visualizing energy flow in natural systems and man-made processes, making them a common tool in environmental and industrial analyses.

Transportation and Logistics

Transport companies use Sankey charts to track the movement of goods and people, illustrating traffic patterns and logistical pathways.

Economics and Business

In marketing, finance, and business management, the volume of information exchange, investments, and transactions can be visualized using Sankeys to show how capital, data, or any other resource flows through an organization.

Social Science

For researchers in fields like demography or complex systems, Sankey charts can show the flows of information, ideas, money, or technology between different groups or states.

Software Engineering

Developers use Sankey diagrams to represent the data flow through their software applications, allowing them to identify bottlenecks or inefficiencies in the code.

With their unique portrayal of the relationships between inputs and outputs in a process, Sankey charts provide depth and nuance that other chart types might omit. Their ability to reveal hidden insights and inefficiencies can lead to improved decision-making and problem-solving in any domain. By combining flowchart elegance with data visualization, Sankey diagrams stand tall as a key tool for those looking to demystify the flow of all kinds of information.

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