What Is an Onion Diagram

An Onion Diagram is a visual stakeholder mapping tool that uses concentric layers to show how internal and external entities interact with the core of a system, project, or organisation. It is used to model relationships, influence levels, and dependencies across multiple operational dimensions.

Each layer of the diagram represents a stakeholder group or system component, with the core element at the centre and increasingly peripheral elements placed outward. This layered approach is ideal for illustrating how closely different actors are involved in an initiative—and what degree of influence they exert.

How Onion Diagrams Work

Onion Diagrams structure information using concentric circles, with the centre representing the most critical process, role, or system element. Outer layers depict indirect contributors or influences. Stakeholders can be grouped according to proximity to decision-making, operational responsibility, or risk exposure.

• Core Layer: Directly responsible parties or systems.
• Middle Layers: Support functions, adjacent teams, or internal stakeholders.
• Outer Layers: External stakeholders, regulators, or wider environmental influences.

Why Use Onion Diagrams?

Onion Diagrams are popular because of their simplicity and flexibility. They help teams:

• Visualise system dependencies and engagement levels
• Clarify stakeholder roles across internal and external boundaries
• Map influence and support functions for better engagement
• Support risk management and project communication

Onion Diagrams in OH&S and ISO 45001

In ISO 45001-compliant OH&S management systems, Onion Diagrams are used to identify the levels of engagement and influence among different stakeholders. This supports Clause 4.2 – Understanding the Needs and Expectations of Interested Parties. It ensures all voices are mapped—from core safety teams to external authorities or affected communities.

Common Use Cases

• Stakeholder Analysis: Visualise stakeholder proximity to core functions.
• Project Management: Assign roles and understand communication pathways.
• Process Mapping: Clarify functional dependencies and systemic interlinks.
• Risk Identification: See which roles are most exposed or disconnected from mitigation plans.

Onion Diagrams vs. Other Mapping Tools

Onion Diagrams are often used alongside other visual tools to provide a multi-dimensional view of stakeholders and systems:

• Power-Interest Matrix – Prioritises stakeholders based on influence and concern level.
• PESTLE Analysis – Captures broader external influences such as legal or political trends.

Combining tools like the Onion Diagram with matrix- or context-based methods allows for deeper insight, particularly in regulatory compliance and OH&S programme design.