The strength of the magnetic field around a long straight wire depends on two things: the size of the current and the distance from the wire.
A bigger current gives a stronger field. If you increase the current, a plotting compass placed at the same spot is affected more strongly. A smaller current gives a weaker field.
The field is strongest closest to the wire and gets weaker as you move away. A compass 1 cm from the wire is affected much more than one 10 cm away. If the field is drawn with lines, the lines are closer together where the field is stronger, so they are packed together near the wire and spread out far from it.
