In one dimensional motion, a point is arbitrarily selected as origin on the straight line along which the body is moving. Points on the right side of this origin (O) on the horizontal line (i.e., x-axis) are given positive sign whereas on the left side are given negative sign
Similarly if the motion is along the vertical line (y-axis) then points upper to the origin are given (+) sign and points lower to the origin are given (-) sign. Position of a particle is given as function of time (say-x) called position co-ordinate. The position co-ordinate can have zero, positive or negative value.