Section 67.   THE CITY PLAN.
   The city council shall adopt a complete plan for the future physical development of the city. Such plan may be altered from time to time. It may include provisions for zoning, for the platting and development of new areas, for the planning and location of public works of art, public buildings, parks, playgrounds, harbors, bridges, transportation lines, and other public facilities, and for the laying out, grading and improving of streets and public places, as well as for all other matters which may seem essential to such a plan.