Michigan Compiled Laws, Chapter 141. Municipal Financing § 141.615

(a) A resident proprietor or partner is taxable upon his entire distributive share of the net profits of the activity regardless of where the activity is conducted.

(b) A nonresident proprietor or partner is taxable only upon his distributive share of the portion of the net profits of the activity which is attributable to the city under the allocation methods provided in this ordinance.

(c) In the hands of a proprietor or partner of an unincorporated activity, the character of any item of income taxable under this ordinance is determined as if such item were realized by the individual proprietor or partner directly from the source from which it is realized by the unincorporated activity. In computing his taxable income for a taxable year, a person who is required to file a return shall include therein his taxable distributive share of the net profits for any partnership year ending within or with his taxable year.