Enlarge publication provided in US city (7)
I believe the answer is:
magnify
'enlarge' is the definition.
('magnify' can be a synonym of 'enlarge')
'publication provided in us city' is the wordplay.
'publication' becomes 'mag' (abbreviation for magazine).
'provided' becomes 'if'.
'in' indicates putting letters inside.
'us city' becomes 'ny' (I've seen this in other clues**).
'if' put into 'ny' is 'nify'.
'mag'+'nify'='MAGNIFY'
(Other definitions for magnify that I've seen before include "Enlarge" , "Intensify, exaggerate" , "Blow up" .)