Flowing Data: How Sankey Charts Visualize Relationships in Data Like Never Before

In the realm of data visualization, the Sankey chart stands out as a powerful tool for representing complex relationships and flows between different categories or entities. Named after Mark Sankey, an engineer who worked for the Edison Machine Works, the Sankey diagram is a type of flow diagram used to visually represent material, energy, cost, or other flow-related data between processes. Sankey diagrams are particularly effective in conveying the distribution, transformation, and movement of items between multiple categories or processes, making them a valuable asset in fields ranging from environmental science to the analysis of supply chains, and beyond.

Understanding Sankey Charts

A Sankey chart consists of several parallel lines (or arrows) that represent different flow types. The width of each line is proportional to the flow quantity. These diagrams are used to illustrate material flows and transformations between processes. In a simplified representation, a Sankey chart might show the input materials and how much gets processed into various intermediate and final products. However, the utility and application of Sankey diagrams extend far beyond simple manufacturing flows. They can also depict energy flows, human flows such as migration, or any category that can be represented as flows.

Creating Sankey Charts

Creating a Sankey chart can be done using various software tools. Excel, for instance, offers an option to create Sankey diagrams through its “Design” tool. However, several dedicated data visualization software and R packages provide more advanced customization options. For example, the Tidyverse package ‘ggSankey’ is a powerful tool for creating Sankey diagrams in R, allowing users to organize data in a tidy format and easily create Sankey diagrams.

Here is a basic example on how to create a Sankey diagram in R using the ‘ggSankey’ package:

“`r
library(ggplot2)
library(ggSankey)

Sample data for Sankey diagram

mydata <- data.frame(
from = c(“A”, “B”, “B”, “C”, “C”, “D”, “D”, “D”),
to = c(“E”, “D”, “F”, “D”, “E”, “B”, “C”, “F”),
value = c(5, 5, 5, 10, 10, 6, 4, 4)
)

Create Sankey diagram

ggplot(mydata, aes(x = x, y = y, fill = category, label = label)) +
ggSankey(flows = mydata, link = list(aesparams = list(width = 0.2))) +
geomtext(aes(x, y – 0.1, label = value), color = “black”, size = 3) +
theme_minimal() +
ggtitle(“Sample Sankey Diagram”)
“`

This code snippet is just a starting point. More sophisticated diagrams may require more complex data preparation and aesthetic customization. The key is to ensure the data is tidy, with a row for each link and columns for the source, target, and flow.

Applications and Use Cases

Sankey charts are widely used for their ability to communicate complex information in a clear, straightforward manner. Here are a few application examples:

1. Energy Flow Analysis: Sankey diagrams are the standard for visualizing the flow of energy in a system, helping engineers and researchers understand energy efficiency and losses.

2. Supply Chain Analysis: By visualizing the flow of materials and resources through a supply chain, Sankey diagrams offer insights that can inform improvements in efficiency, sustainability, and resilience.

3. Healthcare Cost Analysis: In finance, Sankey diagrams can visualize the costs incurred for different stages of healthcare services, such as diagnosis, treatment, and rehabilitation, helping stakeholders make informed decisions.

4. Data Flow Diagrams: Sankey diagrams are useful for visualizing the movement of data between different systems or within a complex data pipeline.

5. Evolution of Populations: In ecology and demography, Sankey diagrams can be used to track the changes in the composition of populations over time, illustrating migration patterns and birth rates.

Conclusion

Sankey charts are a powerful tool for visualizing data relationships in a way that brings clarity to complex datasets. Whether for environmental studies, supply chain analysis, or financial projections, Sankey diagrams offer an insightful and accessible way to understand data flows between multiple categories or processes. As data visualization continues to play a crucial role in conveying information, the utility of Sankey charts continues to increase, making them an essential tool in any data analyst’s toolkit.

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