US city is behind new online map (11)
I believe the answer is:
minneapolis
'us city' is the definition.
(I've seen this before)
'is behind new online map' is the wordplay.
'behind' says to put letters next to each other.
'new' indicates an anagram.
'online'+'map'='onlinemap'
'onlinemap' is an anagram of 'minneapol'.
'is' after 'minneapol' is 'MINNEAPOLIS'.
(Other definitions for minneapolis that I've seen before include "City in Minnesota" , "Saint Paul's twin city" , "US city" .)