This is often asked. To help the understanding of the audience I often use this analogy:
The Enterprise Architect is like a town planner. Solution Architect is designing the buildings in that town.
Thus Solution Architecture starts inside the boundaries defined by enterprise architecture.
With my TOGAF hat on, I would say: Top level Architecture continuum of an organization is defined by Enteprise Architecture. Principles and Artefacts and Reusable Blocks.