When perspective is used, a vanishing point is used. With perspective, parallel lines receding into the screen appear to converge. To make this happen, the process of converting a 3D coordinate (x, y, z) into its 2D perspective on the screen requires dividing the original x and y coordinates by an amount proportional to the original z value. Thus, the larger z is, points on the parallel lines that are far away will be closer together on the screen.