Area of former shelter (6)
I believe the answer is:
extent
'area' is the definition.
(I've seen this before)
'former shelter' is the wordplay.
'former' becomes 'ex' (prefix meaning former or onetime).
'shelter' becomes 'tent' (canvas shelter).
'ex'+'tent'='EXTENT'
'of' acts as a link.
(Other definitions for extent that I've seen before include "Length" , "Compass, scope" , "A cake; last word of Macbeth" , "Area something covers" , "reach?" .)