Cosmology

The cosmology of the Valhalla comics are heavily based on the concept of cosmology as perceived the North Germanic peoples, utilizing sources such as the Poetic Edda and the Prose Edda, however rather than literally having nine separate worlds around or on, above and below the world tree of Yggdrasil, there are three major worlds ordered around the tree in concentric circles, with Asgard in the middle, then Midgard and finally Jotunheim/Utgard. The rest of the traditional seven worlds are instead treated as locations or realms within these three worlds, which are already treated much like different lands on a single plane, some of which are divdided by walls and others by mountains. It should be noted that the idea of the worlds being ordered as concentric circles around the tree is not an invention of the creators of Valhalla, but is a legitimate intepretation of the sources. It is, however, not the most common one.

Mythological background
Norse cosmology is the study of the cosmos (cosmology) as perceived by the North Germanic peoples. The topic encompasses concepts from Norse mythology, such as notions of time and space, cosmogony, personifications, anthropogeny, and eschatology. These concepts are primarily recorded in the Poetic Edda, a collection of poems compiled in the 13th century from much older compositions, and the Prose Edda, authored by Icelander Snorri Sturluson in the 13th century, who drew from earlier traditional sources, some of which are lost, as well as the poems that would later be included in the Poetic Edda. Together, these sources depict an image of Nine Worlds around a cosmic tree, Yggdrasil.