An attempt is made first to describe the solar wind-magnetosphere-ionosphere system in the simplest way in terms of a directly driven system powered by the solar wind-magnetosphere dynamo. The dynamo feeds the Pedersen currents to the ionosphere by generating the field-aligned currents, resulting in the convective motion of the ionosphere and the joule heat production. The field-aligned currents associated with both the Pedersen and Hall currents introduce a considerable complexity to this simple system by generating a potential drop along the geomagnetic field lines. It is also pointed out that the geometry of the open region, namely the polar cap, changes drastically as the BZ component of the interplanetary magnetic field becomes positive. Therefore, one must be cautious in organizing and analyzing data from the highest-latitude region.