Figure 4 is a simplified side view drawing of a slab spanning a ditch. Imagine that you are standing in the ditch, which is wider than it is deep. A line is used to represent the ground level. Reading from left to right, the line starts off straight and horizontal. It then drops suddenly and becomes slightly irregular. The line now represents the steep side of the ditch. The line than becomes horizontal again but is still irregular. The line now represents the bottom of the ditch which is roughly horizontal. The line then suddenly rises and now represents the other steep side of the ditch. When the line reaches the same level at which it started on the left hand side of the drawing, it becomes straight and horizontal again. The slab is depicted by a long narrow rectangle spanning the distance between the two sides of the ditch. Since the drawing is a side view, you know that the slab is longer than the ditch is wide but no exact dimensions are given.