An assurance map is a tool that provides a visual representation of the coverage of risks by various assurance providers. It supports the auditor's decision by showing which risks are being addressed by internal audit and other functions, and which risks are not being tested. This can help justify the auditor's decision not to test a particular risk, by demonstrating that it has already been covered or deemed low priority. Reference:
"Internal Auditing: Assurance & Advisory Services" (The Institute of Internal Auditors)
"Creating an Assurance Map" (IIA Practice Guide)