Thank you to everyone who shared their feedback! We are working on the spec and will share the full details next week. In the meantime, here is a quick update on our direction:
In scope 
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Read-only display: Points, shapes, and traces will be visible while mapping new ones
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Visual distinction: Clear UI so users know these background geometries are not editable
Out of scope (for now) 
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Metadata display: Showing info like creation date or enumerator name for reference
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Real-time overlap constraints: The map won't "block" an overlap in this version
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Layer toggling: Users won't be able to switch these layers on/off manually in the app
We are still refining the colours, stroke weights, and transparency to ensure the best map legibility. Current thinking is that form designers will opt-in to this behaviour, and previously mapped geometry will be displayed by default. Stay tuned for the full spec next week!
Here is a little sneak peek 
Let us know if you have any questions or feedback so far!