Sadly digests opening of this geographical aid (5)
I believe the answer is:
atlas
'this geographical aid' is the definition.
(I've seen this in another clue)
'sadly digests opening' is the wordplay.
'sadly' becomes 'alas' ('alas' is used to express regret).
'digests' becomes 't' (I am not sure about this - if you are sure you should believe this answer much more).
'opening' is an insertion indicator (some letters open a gap in others).
'alas' enclosing 't' is 'ATLAS'.
'of' is the link.
Can you help me to learn more?
(Other definitions for atlas that I've seen before include "A geog. book; N. African range" , "One greatly burdened" , "Cartographer's work" , "travel book" , "In Greek myth, a Titan made to support the heavens" .)
