The purpose of the Architecture Roadmap is to provide a high-level view of how the Baseline Architecture will transition to the Target Architecture over time. It lists work packages on a timeline showing progress towards the Target Architecture, as well as dependencies, risks, and benefits. The Architecture Roadmap forms part of the Implementation and Migration Plan and guides the execution of the architecture projects.
References: https://pubs.opengroup.org/architecture/togaf9-doc/arch/chap20.html