Cartographer

Were you looking for Installation 04's map room, the Silent Cartographer? The Cartographer is Installation 00's map program, similar to Installation 04's Silent Cartographer.

The cartographer building is a Forerunner structure on the Halo rings, which features a map room of an entire Halo structure when activated.

Purpose
The purpose of the Cartographer structure is to show a holographic map which can be used to navigate the massive expanse of area that a Halo is made of. There are similar structures as the Cartographer structure on the Ark which are almost similar shape in exterior and interior on Installation 04 and presumably on all other Halo installations which might have different designs. The map room is somewhat larger than Alpha Halo's Cartographer structure and also much more open to the outside, showing a wide and huge waterfall. This waterfall could be leading to the cooling systems, or could just be a decoration.

The structure is explored in the Halo 3 level The Ark when the player(s) crosses through the Forerunner wall, following 343 Guilty Spark who hacks into the structure to allow him to pass through.

The Cartographer is a much bigger version of the one seen in Halo: Combat Evolved level, Silent Cartographer. There are many structural similarities between the two. They also play the same role, although each on a different scale.

Althrough all this the Cartographer was considered for the Covenant as a great advantage to find the Control Room of Alpha Halo that could explain the presence of Covenant forces near the Map room before the Master Chief arrived to it.

Differences
The differences between the two Cartographers from Alpha Halo and The Ark are the following: On Alpha Halo the Cartographer is situated in somewhat of a cavern in a underground complex where as the one on The Ark is located in a wide open area giving a panoramic view over a massive waterfall. It is clear that each Forerunner structure encountered so far has one of these centers.

Delta Halo, in several ways similar to Alpha Halo, is most likely to have one of these places. These obviously aren't used by the Monitor of the installations itself as they have built-in mapping programmed. These were most likely used by the Forerunners themselves when they would visit one of these installations for any such reason.

This is how characters in the series found the Control Rooms.

Trivia

 * The Cartographer/Silent Cartographer always seem to appear over a chasm.
 * Monitors only have built in map systems of their own installations, (eg. 343 Guilty Spark only has a map of Installation 04) which is why you have to visit a Cartographer on the Ark in Halo 3.
 * The multiplayer level Construct takes place on the cartographer building of Installation 00.