Sankey charts, named after their creator Professor Anthony Sankey, are a type of flow diagram that visually represents the flow of a quantity through a system. These charts are powerful tools for presenting complex data in an intuitive, easy-to-understand format. In this article, we’ll explore the creation of Sankey charts and delve into their various applications, showcasing how they can revolutionize data visualization.

Understanding Sankey Charts

What Sets Them Apart

Sankey charts differ from other diagram types because they emphasize the flow and magnitude of quantities in a system—be it energy, materials, or data flow. In a Sankey diagram, nodes represent stages of a process, while arrows depict flows between those stages, with the width of the arrows corresponding to the volume of the flow or energy passing through.

Components of a Sankey Chart

• Nodes: These serve as the starting and end points of a flow. Each node can have multiple “in” and “out” connections, meaning that a single point in a system can both receive and send data.

• Arrows (Links): These represent the flow of a quantity between nodes. The width of the arrows is proportional to the volume of flow, visually emphasizing the significance of each transfer process.

Key Features

• Magnitude of Flow: The width of the links provides a visual cue for the quantity of flow between nodes, making it easy to spot the major contributors or outputs.

• Node Connections: Nodes can have multiple connections, allowing for the depiction of complex systems and interactions between different components of the system.

• Directional Information: Sankey charts naturally convey the direction of flow in a dataset, enhancing understanding and aiding in the comparison of input and output flows.

Creating Your Own Sankey Chart

Step-by-Step Guide

1. Define Your Data Structure

Before creating a Sankey chart, it’s crucial to understand your dataset’s structure and ensure it contains:

• Sources (Nodes): The origins of your flow.
• Destinations (Nodes): The destinations receiving your flow.
• Flows (Arrows): The volume or other unit representing flow between nodes.

2. Prepare Your Data

• Organize your data: Ensure your data is in a format that can be easily mapped to these components. This might involve cleaning data, such as removing missing values, and organizing data in a structured format suitable for chart software.

3. Select a Tool for Creating Charts

• Choose a tool: Depending on your preference, tools like Microsoft Excel, Tableau, R, Python libraries (such as the squarify or PySankey libraries), and online chart generators can help you create a Sankey diagram.

• Apply Specific Functions: If using Python, for instance, you’ll need to install any necessary libraries (like Sankey) and then apply functions to create your chart.

Example using Python:

“`python
from squarify import squarify
import matplotlib.pyplot as plt
import pandas as pd

Sample data

data = {
‘source’: [‘Node A’, ‘Node B’, ‘Node C’, ‘Node D’],
‘target’: [‘Node E’, ‘Node F’, ‘Node G’, ‘Node A’],
‘value’: [80, 90, 40, 20]
}

df = pd.DataFrame(data)

Plotting Sankey diagram

fig, ax = plt.subplots(figsize=(8, 6))
squarify.plot(sizes=df[‘value’], label=df[‘source’], alpha=0.7)
ax.axis(‘off’)
plt.title(‘Sample Sankey Chart in Python’)
plt.show()
“`

Applications and Real-World Examples

Business Intelligence

• Supply Chain Analysis: To visualize and optimize the flow of materials from suppliers to manufacturers and eventually to the consumer.

Energy Management

• Energy Distribution: Shows how energy moves through an electrical grid, helping in planning and optimizing distribution systems.

Environmental Science

• Carbon Footprints: Tracking the flow of greenhouse gases through industrial processes to highlight areas for reducing emissions.

Economics

• Gross Domestic Product (GDP) Flows: Demonstrating how value is transferred through stages of production, from inputs to final outputs.

Technology

• Data Flow Diagrams: Illustrating how data is processed through different stages of a system, beneficial in designing efficient data pipelines.

Conclusion

Sankey charts are a versatile and powerful tool for data visualization, transforming complex flow patterns into easily understandable diagrams. Whether analyzing energy consumption, tracking the flow of goods, or monitoring data processing, Sankey charts offer a clear and comprehensive view of the relationships and quantities under consideration. As such, their potential applications are vast, and embracing their use can lead to significant insights and optimizations in various industries.

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