When it has been decided to impose any tax on the annual value of holdings, the assessor after making such enquiries as may be necessary, shall determine the valuation of all holdings within the municipality as hereinafter provided, and shall enter the same in a list called the valuation list, which shall be in the prescribed form:
     Provided that valuation other than general valuation may be made by the municipality through such person as may be authorised by the municipality in this behalf.