The 5e terminology requires clarification. Spelljammer is part of the 5e Astral Plane, and players can encounter Alighnment Planes while travelling the Astral Sea. Also many features are now in the Ethereal − Feywild and Shadowfell − rather than in the Astral Plane.
Generally, there is the alignment "plane" as a whole, such Chaotic Good Arborea. But then this plane itself is made out of many planes. An alignment plane can include exclaves, namely islands that are part of the alignment plane yet separate from it..
It helps to refer to an alignment plane as a whole as a "plane". However every alignment planes is actually made out of a network of planar "domains". When diagramming a conceptual map, these domains can have any relationship with each other, but all form portals connecting to each other because, within the mindscape, they all have the same alignment in common. Sometimes one must be in one dominion before finding the access point to an other dominion, hence there is a concept of layers. There can be "layers" of dominions.
For example, the domain of Sigil is inside the domain of True Neutral Outlands.
Comprising parts of Chaotic Good Arborea, the elven dominion of Arvandor "borders" the Greekesque dominion of Olympus, but since one can arrive to one without the other, really both are "first layer" neighbors.
Etcetera.
One can travel by spelljammer to any first level dominion. Visually it is a dominion that appears as an "island" in the Astral Sea. These islands are bigger on the inside than they appear from the outside, sometimes infinitely so. The appearance of these islands look like the drawings of them in earlier D&D Astal maps. One can see the entire mountain of Mount Celestia on its island, with its seven terraces layering upward. Even if trying to reach a higher level directly by spelljammer, it is impossible, it skews either upward above the island or downward onto the foot of the mountain on the island itself. It is spacially anomalous. The only way to reach an upper Celestine dominion is to travel thru the lower dominions indirectly.
Because an alignment plane can have many separate domains, any of these planes by itself can represent the entirety of a alignment plane. For example, in some settings Avandor might exist, but Olympus doesnt exist, or conversely, Olympus exists but Avandor doesnt. An other setting might have something completely different for its Chaotic Good mindscape. This fluidity allows multicultural representation. Any reallife culture can have something that inspires the idea of a Chaotic Good place, namely a place that heightens the concept of "altruism among individualists". This place is for D&D a "dominion" with the mindscape of the Astral Sea.
Certain "dominions" that formerly existed in the Astral Sea in previous D&D editions, now exist as "domains" within the Ethereal. For example, the Eladrin are now natives of the Feywild, rather than Avandor of Arborea. The Eladrin homes are Fey domains. Or rather, the Eladrin governmental courts are now part of the network of "Fey Courts", and each court is its own domain. As natives of the Unaligned Feywild, most Eladrin dont have Chaotic Good alignment, and those who dont would feel little or no personal affinity with Avandor in Arborea, even if Corellon their sacred ancestor happens to be personally Chaotic Good. Thus most "Trances" are about the Feywild, not about Avandor.
Elsewhere, "Hades" used to serve as a name for the Neutral Evil alignment plane. But now since 4e and 5e, Hades is the same thing as the entire plane of Shadowfell. Namely the concept and location of the "underworld", that is any grave individually or grouply. Within the Astral Plane, the Neutral Evil alignment planes does better to go by its other name "Gray Wastes", or perhaps simply "Wastes". Its inhabitants can be Wasters or Wastelanders. Wasters refer to the True Evil alignment that is predatory and via tactics of either Lawful groups or Chaotic individuals exploits and parasites others for ones own gain and at their expense.
The Norsesque areas of Jotunheimr and Ásgárðr are animistic concepts and dont belong in the Astal Plane. They are very much part of the Material Plane. Moreover, assigning the same Chaotic Good alignment to an entire reallife culture is problematic. (I think a "faction" can exhibit an alignment because it comprises conceptual ideals and policies. But to stereotype an entire ethnicity is inevitably a bad game design.) The Norwegian view of Þórr, Óðinn, and Loki is more like Lawful Neutral, True Neutral, and Chaotic Neutral respectively. Probably Þórr has tendencies toward Good, and Loki tendencies toward Evil. These figures are aspects of nature. The fertilizing summer storms, the sky as a whole, and the concept of "entanglement", whence borderlessness, including interactivity, even genderfluidity, as well as trickery and misdirection. Christian traditions associate Loki with the satan as a "deceiver". However, the Norse tales never portray Loki as a liar who says something untrue. Rather, Loki is a trickster who says things that are true but in a way that can outwit opponents.
All of the Norse concepts are animistic ones. One is literally looking at Þórr when looking at anay storm clouds, similar to the way certain American Indigenous are looking at a Thunderbird when looking at a storm cloud. Þórr can project a humanlike form, but is the clouds and lightning literally. In D&D terms, the "hidden" activities of nature beings are happening within the Border Ether. In the context of Fate, the "Primordeal Law" (ørlǫg), the nature beings such as Alfar that orient toward success, life and new posibilities, seem more Fey and are part of the Positive Ethereal Border. Oppositiely, the nature beings such Dvergar that orient toward failure, death and cataclysmic entropy, seem more Shadow and are part of the Negative Ethereal Border. Yggdrasill itself is a cosmic tree, whose ethereal branches spread out over the material known world and whose roots pervade its subterranean. The "Sky" (himinn), also called Ásaheimr, exists ethereally among the clouds, where the clouds are like "wide muck" flung across the branches. However, Ásgarðr is a place on earth, a field on a mountain, a sacred natural landscape feature where the sky beings project from their respective features of the sky, traveling down the rainbow, to the earthy place of their parliament, to vote on cosmic issues.
The Norsesque D&D is Ethereal, including Fey and Shadow, and never away from the Material Plane.
The D&D Plane of "Ysgard" can be something else. The rare Norse term "Ysr", means something like "throng", crowds, tumult. This can be a name for Individualism, where crowds of people would be assisting each other in a bewildering diversity of different ways. But it wouldnt be the Norse places. The "courtyard of a throng", the stronghold of diverse crowds, would be a different kind of concept, orienting more clearly with the concept of Chaotic by Chaotic Good.
In sum, the 5e cosmology is nonidentical with the 3e and 1e cosmologies. There are places that are in different locations, and reallife cultural sensitivities have more priority. There needs to be official clarification.
