Visualizing geomagnetic field with Google Earth
We introduced that the geomagnetic field has origin in an electric magnet excited in the deep inside Earth. The shape of the present geomagnetic field can be loosely approximated by a dipole magnetic moment like a huge bar magnet in the center of the Earth. With more detail observation, however, we can find that the field is not a bar magnet origin but distorted shape.
3D-free-movable compass points a direction which is not the true north and slants upward or downward. The angle between the compass direction and the true north direction in a horizontal plane is declination(positive value for eastward), and the angle between the compass direction and horizontal plane is inclination(positive value for downward).
The maps below indicate the contours of declination and inclination observed on the Earth's surface due to the present geomagnetic field.
So, let's watch the geomagnetic field and its fluctuations with going back from the present!