It is the intent of this article that use regulations and density controls be established for low density single-family residential districts which may be added to the city through annexation. The Planned Residential District provides for somewhat lower density residential single-family development than the R1, R2 or R3 Districts, in keeping with the environmental and topographical characteristics of the hillside areas adjacent to the present city boundaries. It is the intent of this article that developments in areas where these regulations are applicable respect the preservation of unique views which are integral to the natural heritage of the city and the character and density of surrounding areas. The PR District use and density control regulations are intended to apply to new zoning designations subject to full review and approval by the common council of the city. They are applicable to any area which may be annexed in the future by the city where lower density residential development will meet the objectives of this article.