Roll a large map out to reveal a quadrilateral (13)
I believe the answer is:
parallelogram
'a quadrilateral' is the definition.
(parallelogram is a kind of quadrilateral)
'roll a large map out' is the wordplay.
'out' is an anagram indicator (out can mean wrong or inaccurate).
'roll'+'a'+'large'+'map'='rollalargemap'
'rollalargemap' is an anagram of 'PARALLELOGRAM'.
'to reveal' is the link.
(Other definitions for parallelogram that I've seen before include "Type of quadrilateral" , "Four-sided plane figure" , "Quadrilateral with opposite angles being equal" , "Four-sided shape" .)