Part of New York where Mahler composed (6)
I believe the answer is:
harlem
'part of new york' is the definition.
(I know that Harlem has the is part of Manhattan)
'mahler composed' is the wordplay.
'composed' indicates anagramming the letters.
'mahler' anagrammed gives 'HARLEM'.
'where' acts as a link.
(Other definitions for harlem that I've seen before include "Part of New York City" , "Area of New York city" , "some of the Big Apple" , "NY community" , "Father (French)" .)