The whole area covered by the former shelter (6)
I believe the answer is:
extent
'the whole' is the definition.
(thesaurus)
'by the former shelter' is the wordplay.
'by' is a charade indicator (letters next to each other).
'the former' becomes 'ex' (prefix meaning former or onetime).
'shelter' becomes 'tent' (a tent is a kind of shelter).
'ex'+'tent' is 'EXTENT'.
'area covered' acts as a link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for extent that I've seen before include "Scope, area" , "Magnitude - scope" , "Compass, scope" , "Area; size" , "Bulk - compass" .)