District boundaries shown within the lines of streets, streams and transportation rights-of-way shall be deemed to follow their center lines. The vacation of streets shall not affect the location of such district boundaries. When the Zoning Officer cannot definitely determine the location of a district boundary by such center lines, by the scale or dimensions stated on the Zoning Map or by the fact that it clearly coincides with a property line shown on the Zoning Map, they shall deny the application, and the Board, upon appeal, shall interpret the location of the district boundary with reference to the scale of the Zoning Map and the intentions and purposes set forth in all relevant provisions of this chapter. Boundaries of the Conservation District shall extend to the center of any river, or between the upper and lower limits of any slope area which exceeds a grade of 25%.