Citadel Space

Citadel Space is an unofficial term referring to any region of space controlled by a species that acknowledges the authority of the Citadel Council. At first glance, it appears this territory encompasses most of the galaxy. In reality, however, less than 1% of the stars have been explored.
Even mass-effect-FTL drive is slow relative to the volume of the galaxy. Empty space and systems without suitable drive discharge sites are barriers to exploration. Only the mass relays allow ships to jump hundreds of light-years in an instant, the key to expanding across an otherwise impassable galaxy.
Whenever a new relay is activated, the destination system is rapidly developed. From that hub, FTL drive is used to expand to nearby star clusters. The result is a number of densely-developed clusters thinly spread across the vast expanse of space, connected by the mass relay network.
Citadel Space and Charted Space are equal in technology (TL 15), both regions just took different paths to reach their respective Tech Levels.  Charted Space is concentrated in the Orion-Sigma Spur but it contains more Settled Systems than all of Citadel Space.  

Citadel and Charted Space

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This is a map of the major races of Citadel Space in relation to Charted Space.

Geography

Citadel Space developed radially from several Mass Relays.  Civilizations and Colonies are galactically far away from each other but their individual regions were connected by the Mass Relays and they were connected instantaneosly when travelling the Mass Relays.

Localized Phenomena

The Mass Relays as of 1110 are non functional.  Though Citadel Space uses MEFTL(Mass Effect FTL) many of the systems are too far to travel and hazardous due to the static charge that builds up during FTL.  Communication is now conducted as the 3I does so as many Comm Buoys have been destroyed, and those that are in tact have no paths in which to send FTL Messages because the Mass Relays don't work.

History

Currently the Citadel is in orbit around Home.  The Citadel Races that were stranded at Home have begun the very resource intesive rebuilding efforts.  As with the aftermath of the Battle of the Citadel, the Keepers are proving vital in the rebuilding of the Citadel.  It is projected to take 10 years to complete the repairs.

Maps

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  Citadel and Charted Space

  This is a map of the major races of Citadel Space in relation to Charted Space.

Type

Galaxy Supercluster