Flow Matters: Crafting Stories with Sankey Diagrams

Sankey diagrams, a type of flow diagram that visualises data flow along links, are a powerful tool for storytelling, data visualization, and analytics. Named after Mark Sankey, an engineer from the United Kingdom, Sankey diagrams are a versatile visualization technique that allows us to understand the movement of energy, resources, or people from one place to another, and how they are converted or transformed in the process. These diagrams are not just for engineers and scientists; they are increasingly used across various fields, from economics to environmental science, education, and even storytelling. In this article, we will explore how to create Sankey diagrams with the help of Python programming language and discuss their utility in crafting stories with data flows.

Understanding Sankey Diagrams

Sankey diagrams use arrows to represent flows from one value to another. The thickness of these arrows (or links) is proportional to the flow rate (e.g., energy, money, products) between the values they connect. They can also use different colors to differentiate between different material flows, highlighting where and how much the materials change form as they move from one input to an output.

Creating a Sankey Diagram with Python

Python offers several libraries for creating Sankey diagrams, with matplotlib-sankey and caer being two notable examples. In this section, we will focus on creating a simple Sankey diagram using the matplotlib-sankey library. If you are not already set up with the necessary libraries, start by installing them in your Python environment using pip:

bash
pip install matplotlib-sankey[all]


Here’s a basic Python code example on how to create a simple Sankey diagram:

“`python
import matplotlib.pyplot as plt
from matplotlib_sankey import sankey

Diagram parameters

flows = [100, 20, 50, 40, 30, 30, 15, 5]
categorieslist = [“Input”, “Category A”, “Category B”, “Category C”, “Output”]
title = “A Simple Sankey Diagram”
sankey.Sankey(flows=flows, categories=categorieslist, title=title, unit=”units”).plot()

plt.show()
“`

Applications of Sankey Diagrams

Sankey diagrams are particularly useful for visualizing data flows in a system. This can be anything from energy conversion efficiency in a solar panel (how much of the energy harvested is actually usable) to the source of income for an enterprise or the origin of various kinds of investments in a fund. The versatility of these diagrams allows them to narrate complex stories in an easy-to-understand way, making them an excellent tool for education, presentation, and marketing.

Crafting Stories with Data Flows

In storytelling, narratives often involve a journey, a stream of events or information moving from one point to another, leading to a climax or resolution. Similarly, the flow of information can be represented through a Sankey diagram. This could be the flow of information from a single source to different audiences, or the journey of a product from its inception to the market.

Crafting a story with a Sankey diagram involves identifying the key flows (e.g., ideas, resources, energy) and the entities (e.g., processes, organizations, people) involved. You can then use the diagram’s structure to guide the narrative, highlighting key transitions and outcomes.

Conclusion

Sankey diagrams are a powerful tool for visualizing and storytelling with data flows. By understanding how to create these diagrams and recognizing their applications, you can use them to explain complex systems and relationships in a straightforward, engaging manner. Whether you’re a scientist presenting the efficiency of a new energy source, an economist analyzing the flow of investments, or a storyteller weaving a narrative through historical events, Sankey diagrams offer a versatile method to communicate your stories more effectively.

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