Efforts will be made to keep the content simple–we can always make links to more content.
If we run current through a straight wire, we will create a magnetic field around the wire.
We might choose to draw circles showing where the magnetic field is a certain value. For example we might have a circle showing all places where it is 700, 800, 900. You can see this being done on a contour map.
B can have units of Tesla or Gauss.