Extend green plan around city (7)
I believe the answer is:
enlarge
'extend' is the definition.
(thesaurus)
'green plan around city' is the wordplay.
'plan' indicates anagramming the letters (plan can mean organise).
'around' means one lot of letters goes inside another.
'city' becomes 'LA' (Los Angeles).
'green' anagrammed gives 'enrge'.
'enrge' placed around 'la' is 'ENLARGE'.
(Other definitions for enlarge that I've seen before include "Widen" , "Blow up" , "Describe in more detail" , "General (anag)" , "Make greater" .)