"Compass platform" began life as a specific platform upon which a "natural" magnetic compass was placed, so as to get it out of the magnetic influence of the ship.
After the adoption of gyrocompasses, the "natural" compas was used to calibrate the gyros.
That 'master' compass, later on was set up to have a number of electrical contacts which would translate the compase reading into an electrical signal which would inform "repeating" compasses elsewhere aboard.
There was a Royal Navy habit of "conn-ing" the ship from that level due to its elevation. This was above weather decks and without an overhead, giving rise to it being "in the weather." Hence that deck was the Weather Deck, and, later, the Weather Bridge (USN habit from the time was "flying" bridge, as it was above the protected Bridge).
The Brits were slow to "repeat" bridge controls to the weather bridge, which necessitated a number of voice tubes to call orders down to where the helm and "lee helm" (engine telegraph) were located. Also a voice tube from where the Quartermaster was manning the charts.
Charts, being paper and fragile (and precious) were always kept under a roof, often in the structure described as the Charthouse. This was often at the Bridge (Control) level, but could be at the rear of the Weatehr Bridge.
This split-level thing also split how commands work. The officer at the Controlls, was at the "Conn" (traditionally spelt with two 'n'), the commanding Officer, to need would be a deck above.
Forecastle (foc's'l) is the forward quarter of the ship. It can has a reaised deck for handling Ground Tackle. It has been a traditional place where crew were housed ahead of cargo holds.
The term comes from very early ships which had raised battements, tyically a forecastle and an aftercastle from which archers, and later, gonners and cannoniers, "fought" the ship.
In modern use, a ship with a raised forward deck, the entire deck is called the foc's'l. Otherwise, it's the forward potion of the deck to any installed breakwater.