Looking at the elevation plan, we see, first of all, three concentric circles, and inscribed within the inner circle is a square (left) and a hexagon (right). Notice the four points where the square touches the circle, the two points where the middle circle crosses at ground level, and the two points where the outer circle crosses the roof line. Looking back at the floor plan, you can see that the vertical line connecting these two sets of points is the outside walls of the main part of the cathedral.