The Reflected Ceiling Plan tells you whether your Access Point can actually go where you drew it.
Most coverage designs die on the ceiling, not the floor. An AP dropped dead-center of a room looks perfect on the architectural floor plan, right up until the Reflected Ceiling Plan shows a supply diffuser, a light troffer, a sprinkler head, or a soffit sitting in the exact spot.
The Reflected Ceiling Plan is drawn as a mirror of the ceiling, so it carries the grid, the mounting heights, and every ceiling-mounted object you have to design around. Overlay your APs on it and you catch the conflict on paper, where it costs a phone call, instead of at rough-in, where it costs a change order.
Reading the sheet number gets you there fast. US sets follow the National CAD Standard: a discipline letter, a sheet-type digit, a sequence number. A-201 is Architectural, an elevation, first of its type. Plans are the 1 series, so the RCP lives on an A-1xx sheet. Learn the code and you stop flipping through the whole set looking for the one sheet that carries your work.
Why we made this graphic. A designer who can pull the right sheet and speak in sheet numbers gets treated as a peer by the other trades. A designer who cannot gets treated as the Wi-Fi kid who put an AP through a duct. The whole difference is a set of drawing conventions nobody ever sits a wireless engineer down and explains.
Download it, print it, and keep it with the drawing set.
Which sheet do you open first on a new set, and what have you caught on the Reflected Ceiling Plan that the floor plan hid?