2015 New York Laws
GCT - General City
Article 2-D - (General City) CITY PERSONAL INCOME TAX ON RESIDENTS
25-A-11 - City taxable income of a resident individual.

 11. City taxable income of a resident individual.--(a) General.--The
  city  taxable income of a resident individual shall be his city adjusted
  gross income less his city deduction and city  personal  exemptions,  as
  determined under this local law.
(b) Husband and wife.--(1) If the federal taxable income of husband or
  wife  is  determined  on  a  separate federal return, their city taxable
  incomes shall be separately determined.
(2) If the federal taxable income of husband and wife is determined on
  a joint federal return, or if neither files a federal return:
(A) their tax shall be determined on their joint city taxable  income,
  or
(B)  separate  taxes  may be determined on their separate city taxable
  incomes if they so elect and if they comply with the requirements of the
  administrator in setting forth information on a single form.
(3) If either husband or wife  is  a  resident  and  the  other  is  a
  nonresident, the tax of the resident shall be determined on his separate
  city  taxable  income,  unless  both elect to determine their joint city
  taxable income as if both were residents.