A magnetic field is the region around a magnet where another magnet or a magnetic material feels a force. We draw the field using field lines. Outside a magnet the lines have arrows pointing from the north pole to the south pole. The direction of a field line is the direction a free north pole would be pushed.
Around a bar magnet, the field lines are curved lines that leave the north pole and loop round to the south pole. They never cross. The lines are closest together at the poles, so the field is strongest there. Further away, or at the middle of the side of the magnet, the lines are further apart and the field is weaker. So the strength of the field is shown by how close together the lines are: closer together means a stronger field.
A uniform field has the same strength and direction everywhere. It is drawn as straight, parallel lines that are equally spaced. A uniform field can be made in the gap between the unlike poles of two bar magnets, placed close together and facing each other.
