“Zero lot line” means a displacement of a structure toward one lot line after the prescribed height and bulk of the structure have been calculated from setback and height regulations. Such a displacement may be allowed in a planned unit development in R-.1 and R-.25 zone districts where the siting of all surrounding buildings is shown, and only if approved by the city council. The purpose of this reorientation of a building shall be to increase the effectiveness of the open areas. (Ord. 1985-6 § 4 (part); prior code § 5-2-2(PPP))