The magnetic field around a long straight wire is not the same strength everywhere. Its strength depends on two things: the size of the current in the wire and the distance from the wire.
A bigger current makes a stronger field. If you increase the current, a plotting compass in the same place is pulled more strongly and the iron filings make a clearer pattern.
The field is strongest close to the wire and gets weaker as the distance from the wire increases. This is why the field lines are drawn closer together near the wire than further away. Closer lines mean a stronger field. To get the strongest field at a point, increase the current and move the point closer to the wire.
