Pull along North to the metropolis (4)
I believe the answer is:
'the metropolis' is the definition.
'pull along north' is the wordplay.
'pull along' becomes 'tow' (towing is a kind of pulling along).
'north' becomes 'N' (synonyms).
'to' acts as a link.
(Other definitions for town that I've seen before include "Urban community" , "Municipality" , "Milton Keynes, say, with 1a [NEW]" , "Built up area" , "It lies between village and city" .)