An onion diagram is a type of stakeholder map that shows the relative influence, impact, and relation of stakeholders by plotting them closer to or farther away from the solution. An onion diagram consists of concentric circles that represent different layers of stakeholder involvement and interest in the solution. The innermost circle contains the core team members who are directly responsible for the solution. The next circle contains the key stakeholders who have high influence and impacton the solution. The outer circles contain the secondary and tertiary stakeholders who have lower influence and impact on the solution, but still need to be considered and communicated with12.

The other options are not correct because:

A RACI matrix is a type of stakeholder map that shows the roles and responsibilities of stakeholders by assigning them to one of four categories: Responsible, Accountable, Consulted, or Informed. A RACI matrix does not show the relative influence, impact, and relation of stakeholders by plotting them closer to or farther away from the solution3.

A control chart is a type of statistical tool that shows the variation in a process over time and helps to identify the causes of variation. A control chart is not a type of stakeholder map and does not show the relative influence, impact, and relation of stakeholders by plotting them closer to or farther away from the solution4.

A tornado diagram is a type of sensitivity analysis tool that shows the effect of changing the value of one input variable on the output variable. A tornado diagram is not a type of stakeholder map and does not show the relative influence, impact, and relation of stakeholders by plotting them closer to or farther away from the solution5.

References:

Onion Diagram, section “Description of Change”

Stakeholder Mapping 101: A Quick Guide to Stakeholder Maps - ProjectManager, section “Onion Diagram”

RACI Matrix, section “Description of Change”

Control Chart, section “Description of Change”

Tornado Diagram, section “Description of Change”