Who are his users and what does he know about them already? How could he find out more? Who are the stakeholders and what does he know about what they are expecting? How does he want people to interpret the work? What content would help that interpretation? What might distract from that interpretation?

To think through scope and scale, ask yourself: What do people need to understand? What are the edges of the map or diagram? What are you not mapping or diagramming? Where will other people see this map or diagram (e.g., on a wall, in a presentation, on paper)?