The Keeper Compound and Lower Libraries is located by its placement on the west side of the Old Quarter T:DS map.
The colored map alignment is based on its orientation in T3Ed and the in-game compass. (up is north)
The "Keeper Compound" and "Lower Libraries" are separate maps that were connected via a common gateway in T3Ed.
The Thief1 map TG_M1_A_Keeper's_Training is also part of this compound.
General Location: In the City