The position of any given point in a plane can be determined only with respect to a assumed reference point. For practical purposes, the reference point is an intersection of two perpendicular lines. One of them is horizontal and the other is vertical. With the help of these two lines and the reference point, the position of any given point can be determined. As in the above figure location of point P can be described as, 4 units to the right of the vertical seg OL and 3 units above the horizontal seg ON. Here the reference point is assumed to be the beginning or the origin of both, the horizontal as well as the vertical lines. Conventionally having value zero.