Plotting of Magnetic Field
Place a small compass near the south pole of a magnet. The north pole of the compass needle will point towards the south pole of the magnet.
Move the compass roughly to the positions shown in this picture. The compass needle will change direction as you move it.
The direction of the compass needle roughly follows the blue curve.
Move the compass to other positions, and it will follow the directions of other curves.
These curves are called magnetic field lines. They are a way to help us think about the direction of the magnetic force from the magnet.
The region of the space in which this magnetic force exists is called a magnetic field.