Reason to head north, because it's in New York (6)
I believe the answer is:
sanity
'reason' is the definition.
(I've seen this before)
'head north because it's in new york' is the wordplay.
'head north' says the letters should be written in reverse (I've seen 'heading north' mean this (in a down clue, letters travel north)).
'because' becomes 'as' (I've seen this in other clues).
'in' indicates putting letters inside.
'new york' becomes 'ny'.
'as' in reverse letter order is 'sa'.
'it' inserted within 'ny' is 'nity'.
'sa'+'nity'='SANITY'
'to' is the link.
(Other definitions for sanity that I've seen before include "Sound powers of mind" , "Mental wellness" , "Good sense" , "Soundness of mind" , "Balance of mind" .)