The magnetic field around a current-carrying wire is not the same strength everywhere. Its strength depends on two things. The first is the current. A larger current in the wire makes a stronger field. The second is the distance from the wire. The field is strongest close to the wire and gets weaker the further you go from it.
This is shown by the field lines. They are drawn as circles around the wire. Near the wire the circles are closer together, so the field is strongest there. Further out the circles are spread apart, which shows that the field is weaker.
To investigate, place a plotting compass at different distances from a wire and watch how far the needle turns. The turn is bigger when the compass is closer to the wire or when the current is larger. To make the field at a point stronger you can increase the current or move the point closer to the wire.
