Harmonian Earth is the equivalent of Earth in the Harmonia universe. It consists of two layers- Lower Earth and Skylands. Lower Earth is the Earth we all know- modern tech, normal people, environmental problems, et cetera. Magic from Skylands cannot leak down here, so it is not magically-influenced at all. Skylands is the magical part of Earth, and it consists of a massive array of floating islands, filled with magical energies and alien species.
It was divided into Lower Earth and Skylands long ago, after an insane magical accident tore pieces from the earth and sent them into orbit. They now float within the atmosphere, imbued with magic. After this occurred, magic was banned in Lower Earth.