A magnetic field is the vectorial magnitude that expresses the intensity of magnetic force. The magnetic field is created by electrical charges in movement, but it's never created in the same direction as the trajectory of the charge. Further, charges at rest do not originate any magnetic field.
The Earth behaves as a gigantic magnet and has magnetic poles:
The unit of measurement of the density of magnetic flux is tesla, and it is represented by a capital letter T.
1T = Wb/m2
1T = 10000 Gauss
1nT = 10-9T = 105G
The Earth's magnetic field is approximately 1 Gauss (G)