Iowa Code § 331.210: Plan “three”.

If plan “three” is selected pursuant to section 331.206 or 331.207, the supervisor districts shall be drawn and supervisors shall be elected as provided in section 331.209, except the boundaries of supervisor districts shall follow voting precinct lines and each member of the board and each candidate for the office shall be elected or nominated at the primary and general elections by only the electors of the district which that candidate seeks to represent.