Explain the poem's final conceit about the hemispheres of a planet.

In its final six lines, the poem compares the two lovers to the separate hemispheres of a single planet. Each is territory the other can explore--but each is also somehow incomplete without the other. These "hemispheres" are superior to those of the real world, because they are not cold like the Northern hemisphere or symbolic of death and decay, like the Western hemisphere (where the sun sets.) The implication is that the world of love these two lovers create between them is perfect and immortal.