each square is roughly 18 square miles
This is about the those land masses and the people living on them.
By an internal logic similar to Aristotle's striation of the sublunary sphere into concentric elemental slices, the biomes sinking around the Slaad are oriented to one another by temperature, climate and native life such that the temperate biomes often agglomerate into a band on which either side is a more tropic and more arctic band. This isn't universally true and fingers of ocean - impossibly deep cracks teeming with ocean life - span biomes and offer routes for trade, transport and communication (both via sail and submersible, especially the latter, as many share subsurface tributaries). Similarly, deserts and arctic cankers may sit in the middle of a jungle and while, over long centuries, each biome wanders along its borders and the oceans spread and swallow deserts and jungles flood or dry out, natural processes are much too slow and the inevitable inclination toward ultimate dissolution and end in the primal soup of Limbo prevents more serious transition.
Tectonic action occurs here too as the Slaad shifts or the Limbic body, both like an ocean and a plate, rubs against the Slaad's crust of biomes, but at the level of biome (one biome interposed over another in quick tectonic action - what life can survive in that new place doing so, most of it dying off, most such under-places being complexly dead in a generation or two).
More jumbled: the agglomeration of biomes can be both vertical and horizontal, meaning that there may be forests under forests (one the mirror of the other, their roots tangled or else actual layers where the roof of one is dotted with the root-tips of the other) or a forest swallowed by a swamp. The inhabitants of the Slaad's districts refer to upper- (lit by the weird light of the Slaad's mind palace) and under- (usually lightless). Oceans may fill such undertructures, but many are dry.
The gentry of the Witchocracies that populate Slaad-touched swamps talk of going to under-forest and upper-swamp, and weave into their long black hair the little bones of the birdlike and lamp-eyed goblins that roam those lightless woods. Some such places are lodged like a bezoar and have petrified, bushes like sharp grey teeth to the touch, or are otherwise well preserved, treasure troves of older technologies.
The city-states of the Slaad lands (Ariesne-Orlay, the Atlantis-Ys Protectorate, Kievs) all have on lease from Gaz'sham traitor-pirates drill-tanks, boring rigs, assaying instruments the size of a house, are seeking caches of lost technology sufficient to kill or incapacitate their Slaad or one another or rocket themselves either out Limbo or at least keep them from sinking further.
The closer a biome is to the Slaad or the Limbic body, the greater the variation, the greater the deformation due to radiation.
Each biome pulled from the material plane tends to be in a state of natural decline even before its capture. Accordingly, any civilizations and peoples brought with their homelands are usually living in ruins, People living among technologies they no longer understand in a land that has turned against them:
"Had satellite imaging existed, those distinguishing features of civilized life - towns, roads, cultivated expanses - would have been mostly invisible to the camera eye under their canopy of primeval growth. Beneath the green scrim, millions of wolves roamed the twilit forests, packs prowled the rutted streets..." (God's Crucible pg 152-3)
What remains: roads left to the depredations of forests, roots and erosion, and the casual habitation of highwaymen and independent tollbooths, aqueducts full of stagnant life and weeds, their vast cisterns home to salinae burbling water songs in brackish or water-goblins making earth-bombs at the behest of beings vast, ancient and aqueous, factories (into which teams journey to salvage metal) in which lurk old guards in rusting armor and books of inscrutable power, museums and laboratories to be ransacked for arcanum and histories, castles being squatted in by revolutionaries or sorcerers looking for help or people to use or someone to do some nasty work, cities teeming with people from a multitude of biomes and planets, refugees from a collapsing or long lost biome.
Memories of one's home being taken by the Slaad are consonant with myths of cataclysm and apocalypse; Slaad capture mechanisms are as different as possible from the subtle engagement of Ravenloft.
Xaositect cells pamphlet civilized areas, establish dischoirs, overthrow tyrants and recruit the more democratically inclined.
Over all this looms the Slaad, and over the Slaad, its mind palace, radiating psychic abreality and chaos and entropy, a forever mouth and gut swallowing whatever is around it, pullulating monstrosities, Slaad-intention spreading over the sky like a foul borealis moving in waves of mutation. This is a place from which the eye is averted, to which no maps lead, but to which every compass points.
Slaad mind palaces are like machines, massive circuits of chaos and maleficence, its hooks and conduits like flumes into other planes, chutes down into a gnawing and total chaos, its few pools and more still chambers huge networks like dungeons, teeming with nastiness, mutation and horror, hordes of psychic weapons and engines.
And into which come Xaositect Legions on their continent-ships, nothing offends them more than the vestigial order and civilization that clings to Slaad land masses and they often attach great weights or engines to drive these masses into the primal soup at a much accelerated pace.
Some Slaad share biomes at their extremes, most, however, do not and at the far end of any biome is what appears to be a vast sea of alien, inhospitable landmasses floating according to obscure tectonic action, swallowing and shitting out one another like amoeba, blind and idiot flagella, geometries that sicken the mind, over which or through which crawls the black ships of Gaz'sham or the cumbersome 'zerai missile boats.
Slaadland peninsula into the Limbic body