Visibility at Intersections. On a corner lot in any residential zone, nothing shall be erected, placed, planted or allowed to grow in such a manner as to materially impede vision between a height of two and one-half (2 1/2) feet and ten (10) feet above the center-line grades of the intersecting streets in the area bounded by the street lines of such corner lots and a line joining points along said lines thirty (30) feet from the point of intersection, nor shall a principal structure be located less than twenty-five (25) feet from the side street line.