Before the construction of any boulevard and before the calling of any election for the issuance of bonds, the commission shall employ one or more engineers who shall make all necessary surveys, prepare maps showing the location, cross-section and profile of the proposed boulevard. The engineer shall also prepare specifications for the construction of the boulevard and estimates of the cost of construction and of acquiring rights of way.

These surveys, maps, specifications and estimates shall, upon approval by the commission, be formally adopted by order entered upon its minutes and filed with its secretary and when so adopted shall constitute the plan of the district for the proposed boulevard. The commission may, at its option, direct the county surveyor, or county engineer, as the case may be, to do any of the engineering work.