This photo provides a good side view of a slope; note that the top half is convex (curves down) & the bottom half concave (curves up). The point where convex meets concave is called the keyline & if you look carefully, you will notice several of these points here. We can use such information in our design to help us to place buildings, water collectors, plantings & so on. Note too that the steep slopes are forested to prevent erosion.