What Is an Onion Diagram

Understanding Stakeholder Layers and System Dependencies Using Onion Diagrams

Updated March 2025

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.

Why Use Onion Diagrams?

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

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

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:

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.

Onion Diagrams help illustrate who or what is closest to a system’s core activity, and how other components or stakeholders relate in influence or dependency.

Unlike matrices that rank stakeholders by influence or interest, Onion Diagrams show relational proximity to a core process or issue, making them ideal for visualising engagement layers and systemic roles.

The diagram supports ISO 45001 by identifying all interested parties and how closely they relate to OH&S risks, systems, or outcomes—meeting the intent of Clause 4.2 and enhancing stakeholder awareness.