Flow Analysis Made Easy: A Journey Through Sankey Diagrams

Sankey diagrams, named after the Scottish engineer and civil engineer Matthew Henry Phineas Riall “Sankey”, are a special species of flow diagrams. They utilize rectangular bars, also called bands or strips, to represent flows in different sizes and directions between various nodes. This graphic model is extensively used in fields like engineering, economics, and natural sciences to visualize large, complex data sets and illustrate system interactions. In this article, we will embark on a journey to understand and create Sankey diagrams, as well as their wide-ranging applications.

Purpose of Sankey Diagrams

The primary goal of Sankey diagrams is to simplify and represent the flow of quantities from one place to another. They can be used to visualize a variety of data types:

1. Resource management: Tracking the flow of materials, energy, or data in a system.
2. Economic analysis: Examining the flow of money between industries or countries.
3. Energy sector: Showing the transfer between different energy sources or consumers.
4. Social sciences: Analyzing the movement of individuals between organizations or geographical regions.
5. Health sciences: Examining the flow of patients between hospitals or healthcare providers.
6. Environmental science: Tracking the flow of pollutants or natural resources through different ecosystems.

Sankey diagrams are particularly effective for illustrating data that has a hierarchical structure, where the width of the bands represents the magnitude of the flow. This visual representation makes it easier to compare the sizes of flows, identify top contributors, and spot connections that might be less obvious in tabular data.

Components of a Sankey Diagram

A Sankey diagram has three main components:

1. Nodes: These are the points where flows enter, leave, or pass through a system. Nodes represent the different entities involved in the flow.

2. Arrows: These are the connections between nodes, which represent the pathways of the flow. The direction of the arrows indicates movement from one node to another.

3. Bands or Rectangles: These represent the flow of quantities between nodes. The width of the bands visually corresponds to the magnitude of the flow. The color of the bands can be used to indicate categories or differentiate flows based on different criteria.

Creating a Sankey Diagram

Creating a Sankey diagram involves three main steps:

1. Data Collection: Gather the data you want to represent. This typically includes source nodes, target nodes, and the flow quantities between them.

2. Choosing a Tool: Select a tool or software to create the diagram. Many options are available, including:

   • Data visualization libraries in programming languages like Python (e.g., Plotly, Matplotlib), which offer Sankey diagram functions.
   • Spreadsheet software such as Microsoft Excel or Google Sheets, which can provide built-in chart types for Sankey diagrams.
   • Specialized data visualization tools like Tableau, which have dedicated Sankey diagram functionalities.

3. Design and Customization: Customize the appearance of your Sankey diagram to clearly communicate your data. Adjust properties such as band width, color, and labeling to enhance readability and focus on important aspects of the data.

Applications of Sankey Diagrams

Sankey diagrams find applications across multiple fields because of their ability to represent complex data with clarity:

1. Engineering and Manufacturing: To track material flows and energy use through production processes, facilitating improvements in efficiency and resource management.

2. Environmental Science: To visualize the movement of pollutants between regions, helping in environmental conservation and policy-making.

3. Economics: As economic flow diagrams, they illustrate trade relationships, aiding in policy analysis and forecasting.

4. Healthcare: To assess the flow of patients through a healthcare system, identifying bottlenecks and areas for improvement.

5. Urban Planning: To analyze the distribution of resources like water, electricity, and vehicles, making urban systems more sustainable.

6. Business Intelligence: In sales and marketing, Sankey diagrams can illustrate customer journey flows, identifying key touchpoints and conversion patterns.

7. Data Science: To analyze and visualize complex data flows within data processing pipelines, enhancing understanding of system performance and potential optimization areas.

In conclusion, Sankey diagrams are a powerful visualization tool that can help demystify a wide range of data flows and transform complex information into visually intuitive and easily understandable insights. By embracing Sankey diagrams, professionals across various disciplines can harness data-driven insights to make informed decisions, optimize processes, and guide strategic planning.

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