The city council shall, at the time of making the next general tax levy and in the manner provided for the general tax levy, levy a special assessment tax upon all lands, and may at such time and in such manner levy a special assessment upon all improvements, within the district, and within any zone therein, which will be sufficient to raise that portion of the estimated cost of the improvement for the next year which is to be borne by the district.

The city council shall state in its levy whether the special assessment is upon all land within the district or upon all land and all improvements within the district.