1. More than one project may be combined in one improvement district when the governing body determines such projects may be combined together in an efficient and economical improvement district.
2. If in the combination of projects, they shall be separate and distinct by reason of substantial difference in their character or location, or otherwise, each such project shall be considered as a unit or quasi-improvement district for the purpose of petition, remonstrance and assessment.
3. In case of such combination, the governing body shall designate the project and area constituting each such unit, and in the absence of an arbitrary and unreasonable abuse of discretion, its determination that there is or is not such a combination and its determination of the project and area constituting each such unit shall be final and conclusive.
4. The costs of acquiring or improving each such project shall be segregated for the levy of assessments and an equitable share of the incidental costs shall be allocated to each such unit.