Flow with Style: Unveiling the Power of Sankey Charts
Sankey diagrams, named after their inventor, engineer Sankey, have evolved from an engineering tool for visualizing energy flow in steam engines to a versatile and powerful visualization method in finance, environmental science, and many other fields. These charts are not merely a nostalgic nod to early 20th-century design; they are a modern and essential tool for presenting complex flow data in a clear and accessible manner. In this article, we will explore how Sankey charts have evolved, how to create them, and their diverse applications in today’s world.
Understanding Sankey Charts
Sankey diagrams depict the direction and flow quantity between nodes in a network. They are a type of flow diagram, allowing for the visualization of the direction and quantity of flows between different compartments of a system. The primary feature of a Sankey chart is its set of parallel bars, each representing a single flow. The width of each bar is proportional to the flow quantity, making it easier to grasp the magnitude of data visually.
The Evolution of Sankey Charts
The first Sankey diagram was created by John Merle Farquhar in a paper published in the Transactions of the American Institute of Electrical Engineers in 1918. However, it was John Snow who popularized the use of Sankey diagrams in epidemiology with his 1854 map of the Broad Street cholera outbreak. Today, Sankey diagrams find use in a wide range of applications and are frequently used in data visualization for their clarity and the insight they provide into complex systems.
Creating Sankey Charts
Creating a Sankey chart begins with organizing your data into a tidy format. The data typically consists of multiple variables: the source (what is transferring), the target (where it is transferring to), and the value (how much is transferring). Once your data is clean, you can use programming languages like Python, R, or JavaScript to create a Sankey diagram. Libraries and tools such as Plotly, Bokeh, and Altair provide easy-to-use interfaces for creating and customizing Sankey diagrams.
To create a basic Sankey diagram in Python using Plotly, you would organize your data in a DataFrame with columns for source, target, and value. Then, you can use Plotly’s go.Sankey function to generate and display the chart. Here’s a simple example:
“`python
import plotly.graph_objects as go
Organize your data into a tidy format
df = pd.DataFrame([
[‘Energy source’, ‘Process 1’, 50],
[‘Energy source’, ‘Process 2’, 30],
[‘Process 1’, ‘Output product’, 45],
[‘Process 1’, ‘Output waste’, 5],
[‘Process 2’, ‘Output product’, 30],
[‘Process 2’, ‘Output waste’, 10]
])
Reshape your data into a tidy format for Sankey diagrams
dfsankey = df.melt(idvars=’Energy source’, value_vars=[‘Process 1’, ‘Process 2’]).rename(columns={‘Energy source’: ‘Source’, ‘value’: ‘Value’, ‘variable’: ‘Target’})
Create and display the Sankey chart
tracesankey = go.Sankey(
node = dict(
pad = 15,
thickness = 20,
line = dict(color = “black”, width = 0.1),
label = dfsankey[‘Source’].unique(),
color = ‘rgba(169, 169, 169, 0.8)’
),
link = dict(
source = dfsankey[‘Source’],
target = dfsankey[‘Target’],
value = df_sankey[‘Value’]
)
)
layout = go.Layout(title = ‘Simple Sankey Diagram’, showlegend = False)
fig = go.Figure(data = [trace_sankey], layout = layout)
fig.show()
“`
Applications of Sankey Charts
Sankey diagrams are incredibly versatile. They are used in a variety of applications, including:
- Energy Systems: Analyzing energy flows through different stages of use.
- Ecological Footprints: Quantifying inputs and outputs in supply chains.
- Environmental and Health Studies: Visualizing disease transmission or environmental pollutants.
- Project Management: Tracking project resources and flow through different phases.
- Economic Evaluations: Representing revenue flow between different products or services.
Conclusion
Sankey diagrams have evolved from their historical roots to become a powerful tool in today’s data-driven world. Their unique ability to visualize complex flow relationships makes them invaluable in fields where understanding the nuances of flow data is critical. Whether you’re in energy analysis, environmental science, or financial analysis, understanding how to create and interpret Sankey diagrams can provide a deeper insight into your data. And as technology and data visualization continue to evolve, the role of the Sankey chart in our understanding of complex systems is likely to grow even further.
SankeyMaster
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