What is Sankey Diagram?
A Sankey diagram is a flow chart where the width of each arrow or band represents the size of a flow between nodes. It visually shows how quantities move between states, categories or stages.
A Sankey diagram maps movements or transfers — for example people, money, material or responses — from one set of categories to another. Each node represents a state or group (such as a survey question, channel or outcome) and the links between nodes are drawn as bands whose width is proportional to the amount flowing along that connection. Sankeys are usually read left-to-right (source to destination) and are useful when you want to show proportions, where the largest pathways are and how multiple sources combine or split into different results.
Usage example
A local council uses a Sankey diagram to show how residents reached a consultation (email, leaflet, social media), which language they chose to respond in, and whether they completed the survey or dropped out — the widest bands reveal the most common paths.
Practical application
Sankey diagrams make complex transitions easy to understand at a glance. For Hearo users they can reveal patterns such as which outreach channels generate responses in particular languages, where participants abandon a form, or how language groups distribute across service outcomes. That information helps teams prioritise translation audits, improve question wording for groups who drop out, allocate outreach resources, and tell a clear story to stakeholders. Note the trade-offs: Sankeys highlight major flows well but can become cluttered with many small categories and are better for showing relative flows than for communicating precise numeric detail.
FAQ
How do you read a Sankey diagram?
Follow the bands from left to right: the position of a node shows its role (source, intermediary, or destination) and the width of each connecting band shows the relative quantity moving along that path. Wider bands mean larger flows.
When should I use a Sankey instead of a bar or pie chart?
Use a Sankey when you need to show movement or transitions between categories (for example, referral source → language → outcome). Bar and pie charts are better when you only need to compare totals or proportions within a single category.
What are common limitations of Sankey diagrams?
They can become hard to read with many nodes or lots of small flows, they emphasize relative rather than exact values, and layout choices can affect interpretation. It helps to simplify categories, aggregate rare flows, and provide numeric labels or a companion table for precise figures.