Position of any point is completely expressed by two factors : Its distance from the observer and its direction with respect to observer. That is why position is characterised by a vector known as position vector. Let point P is in a xy plane and its coordinates are (x, y).
Then position vector (r) of point will be xi + yj and if the point P is in a space and its coordinates are (x, y, z) then position vector can be expressed as r = xi + yj + zk.
