Fix a sheet of paper on a drawing board or a table means of brass pins. place a small  compass needle and mark two pencil dots exactly at the two ends of the needle.then move the compass needle in such away that one end of the needle coincides with the second pencil dot.mark the position of the other end of the needle with a dot.repeat the process of moving the compass needle to obtain several dots .join the different dots to get a straight line as shown in below figure.thus one line of magnetic field of earth is traced.label each line with an arrow from the north pole towards the south pole of the magnet to indicate its is noticed that these lines do not cross each other.they are parallel and equi-distant