Clusters are natural areas of pocket dimensions inside the Blue Channel, consisting of levels physically close to each other due to their similarity in how Liminal Echo influenced their structure.
Cosmology
These formations can be compared to galaxies of pocket dimensions in the wider Backrooms universe.
Levels from the same cluster share thresholds1 between each other, while links between clusters are much rarer. This effectively makes cross-cluster communication extremely hard in most situations2 (?)
The space in the Blue Channel between clusters is usually pure emptiness, with only a few lone levels existing there, sometimes without any existing access. It is possible these lone pocket dimensions are new clusters, slowly but surely growing due to their respective affiliated country cultures in the Frontrooms developing themselves (see Formation below).
Due to the 11-dimensional nature of the Blue Channel, overlaps between clusters can exist in a similar manner to how overlaps inside them can be formed3. In the case of clusters, their folding point is the enigmatic area nicknamed the Archipelago by its discoverers. Consisting of islands each reminiscent of the architecture and terrain of a specific culture, it nevertheless remains a difficult to access hub-like level, which makes clusters-related research tougher due to its dead-end nature.
Formation
The formation of clusters in the Blue Channel is tied to Liminal Echo, as as such, to the Frontrooms human conciousness.
Nostalgia can very greatly between civilizations, and it is these very variations that allow for clusters to exist. The more widespread a culture is, the more people will experience anemoia tied to their respective architecture or way of life. As such, levels created by their collective conciousness will, over time, move closer together, leading to more dimensional overlaps.
Population and Frontrooms links
The human factor goes beyond cluster's creation however. Over the centuries, it has been noted that, statistically, people tend to initially noclip in their respective cluster. While this isn't a consistent phenomena4, this seem to indicate that wanderers usually evolve in levels reminiscent of their own vision of nostalgia, strengthening its liminal aspect.
Below can be found a list of each known clusters, with their respective imagery and cultural liminal significations:
Francophone Cluster
Pictures of different francophonic levels of the Backrooms.
Interestingly enough, the Francophonic cluster has almost entirely merged with the English cluster, as if they collided over time. This unique case across all cultural clusters is theorized to have resulted in the wider Americanization of France during the Cold War era, the country indeed having been the second biggest recipient of the Marshall Plan during that era, which caused the architectural and cultural effects of globalization to be exacerbated. Level architectures such as on Level 8-FR can be traced back to this.
With that said, this doesn't mean Francophonic levels do not exist, as many levels display typical French architecture. Hausmannian buildings, an architectural style of the Second Empire that spread in the country during the second half of the 19th century, are a common occurrence, such as on Level 48-FR. Similarly, the presence of historical building replicas can also be noted, such as on Level 2-FR.
Mainland France isn't the only Francophone culture to be represented in the architecture of the Francophone cluster, as levels such as Level 44-FR feature a Belgian-looking countryside reminiscent of the 1940s.