Giant book of maps (5)
I believe the answer is:
This clue is a triple definition!
'giant' is the first definition.
(I've seen this before)
'book' is the second definition.
(atlas is a kind of book)
'of' acts as a link.
'maps' is the third definition.
(printed collection of maps)
(Other definitions for atlas that I've seen before include "Album of maps" , "I carry a huge weight" , "Large-format book" , "Supporter of the classics" , "Sky carrier - map book" .)