Quick polity and biome procedures for approaching strange worlds

From the previous post on randomly generating a system I was left with the puzzle of what to do with truly enormous planets with mind boggling surface areas. What can you pack into a water world the size of Saturn, for instance? For reference, Earth is the archetypal Class E, but we have 30% of our surface above water so only 60M square miles. That is to say the next class down, D, has half the land area of our Earth, assuming there are no surface water bodies at all. For reference, the planetary classes and their areas if a sphere or a single-sided discworld.

Class	Diameter (mi)	Sphere surface area (mi.sq)	Discworld top side area (mi.sq)
A	350	384845	96211
B	800	2010619	502655
C	1500	7068583	1767146
D	3200	32169909	8042477
E	8000	201061930	50265482
F	16000	804247719	201061930
G	32000	3216990877	804247719
H	80000	20106192983	5026548246
I	160000	80424771932	20106192983
J	350000	384845100065	96211275016

To try and visualise this - here is a cumulative area chart, assuming an Earth-like share of ocean coverage (70%) - red is Class E - Earth - down in the corner. Once you move up a planetary size class, you start getting some very large spaces to work with indeed.

The question that arose elsewhere was 'does this mean a planet is a mono-culture?' I see argument in some places saying that if you are running Spelljammer or any other inter-planetary game then there is no point creating highly detailed worlds because you want getting from point to point to be part of the fun of the setting. The detail and interest on a given world should not be so much that people decide to stay groundside and abandon the Spelljamming part of it all. Taking that on board, I think there is a question of versimillitude - I can see the typical table I run giving me a very hard stare if I said 'there is no geographic variation on this world' and 'a single polity rules everything' for a place the size of Earth.

Coming back to our question of mono-cultured worlds - for A, B and C class planets I think we can say probably yes. There have been many empires in the history of the Earth that have encompassed this size of territory so assuming a unitary culture over that area is not beyond reason. Class D planets are about at the top end of what we see historically for Earth but let us simplify our workload and say they too are 'one-thing-happening-here' places.

What about the other end of things - what about places with more surface area than Earth - either through less oceans or bigger planet size? The big variable here is the geography of such worlds - whether land areas are split up as continents or islands or subdivided by terrain features that would isolate populations. Given that most of the adventures in 5e Forgotten Realms happen within the Sword Coast - a region of one continent - and that there are three significantly detailed other regions (Zakhara, Kara-Tur, Maztica) and four lightly detailed outlying regions (Anchorome, Katashaka, Laerakond, Osse) - we see that in 12% of the world, we get lifetimes of adventuring. How valuable is it to even try to detail up what is happening on these larger worlds? I suggest for the purposes of making world creation a manageable task you can take two approaches - a) the kitchen sink and b) the scaled-up Earth.

For a) we assume this place is big enough that you can have anything you like in it and just go hog wild. Assume mountains, seas, deserts and the like keep the things you want to have in there conveniently seperated. Sitting in a place where there are 3 nations within an hours drive, 6 within 3 hours drive and coming from a place where the accents change every hour down the road, I feel comfortable that this is a reasonable approach if you want to go with it.

"Go with whatever you like" is fine but what if your players are bouncing around a lot and you want to simplify things with some sort of procedure? If we look at how much terrain empires in various periods of human history controlled as contemporaries to one another we can identify a few pre-industrial periods with a similar trend - the largest empire around controlled ~ 10% of Earths area, then the next controls 6-10%, the next ~4% and then smaller contemporaries dropping away from there. The largest pre-industrial empire was the Mongols, by a long way, controlling 18% of the Earth. Post industrialisation we see empires achieve that kind of territory again, with the largest of all time being the British Empire at 26%. If we batch empires with their contemporaries we can sketch out a trend that roughly matches and gives us a group of 10 contemporary polities that control ~ 70% of the surface of the Earth.

If we move up a size class to F - suddenly all that is trivial. Assuming similar ocean coverage we still have four times the dry land and our 'reasonable group of assumed empires' goes from controlling 70% of it down to 18%. Let us assume that through magic, our polities can exert twice the area of control that historical Earth equivalents could - still we have on 36% of the planet accounted for. Perhaps long-lived of fast-moving races could increase their holdings - giants cover more ground in a stride, elves stick around longer to consolidate things - and get us back to this same balance again. All this still says that we should have at least the same level of diversity of nations and peoples on any of these larger worlds, even if we are dealing with elves, giants, dwarfs or other races that you might expect to tend towards a monoculture.

What if we move up another size class to G? Now our original reasonable group of contemporary empires can cover 4% of the surface. These places are mind-bogglingly huge, 16 times the surface of the Earth. 16 times the diversity of Earth on one world. This to me says that if a shipload of Spelljamming adventurers just land at random on one of these places there could be anything there to meet them. You could literally have a dark overlord controlling an area the size of the surface of the Earth - and still have vast amounts of room on the planet.

For b) I would suggest turning to our old friend the power curve and go with the following table:

Region Controller	d100
Primary power	1-19
Great rivals	20-24
Great rivals	25-28
Great rivals	29-31
Regional power	32-33
Regional power	34-35
Regional power	36
Regional power	37
Regional power	38
Regional power	39
Smaller realms	40-71
Hinterlands	72-100

If this is a time of significant change, the Primary Power can be come 3 Great Rivals of roughly equal size. In each case, if the number rolled is the lowest possible for that entry, this is the heartland where that power originated from - everything else means it is a possession of that power - on more or less friendly terms as you see fit. 90% of Earths population is on 10% of the land so we shall say that the 10 heartlands of these realms also have most of the population on this planet.

On a relative scale - the primary power would be like the Mongols, the Spanish Empire, Qing Dynasty or the British Empire at the height of their powers - their presence was felt by the others even outside their realms - either as conquerors, guarantors of trade or the well-spring of riches. Most likely to have access to Spelljamming and be aware of off-world affairs whether or not they are actively involved.

Great rivals would be near-peers to the primary power in wealth, might and ambition, significant powers in their own right and able to set their own path. Often to be found causing trouble for the Primary power to keep them from growing still more mighty. They may also have Spelljammers or may even be ahead of the primary power as a way to maintain a balance of power.

Regional powers would be dominant in their local region but vulnerable to either the great rivals of the primary power should they choose to attack them. Depending on the defensibility of their lands these might be more or less paranoid about spies and new arrivals.

Smaller realms may be more or less sophisticated or isolationist - welcome can vary hugely - can be a dragons territory, an isolated tribe, a wizard in their tower.

Hinterlands are wilds where the terrain does not allow significant settlement. Nomads may dwell here but you will find few if any permanent settlements.

For a Spelljammer on approach to a new world, if they look for signs of habitation and activity and head towards that, you can roll a d6 for the 'tens' of the d100 to get a 1-60 result.

Lastly, whatever the size of the world, for a quick and dirty sense of regional climate variation I suggest the following:

Biome	d100
Mid temperature, wet, stable climate, abundant life	1-22
Mid temperature, wet, highly seasonal, abundant life	23-41
Hotter, drier, sparsely inhabited	42-56
Cooler, wetter, sparsely inhabited	57-65
Hotter, wetter, abundant life	66-70
Hotter, drier, abundant life	71-71
Coldest, dry, sparsely populated	72-86
Hottest, dry, sparsely populated	87-100

This is roughly equivalent to Earth in its proportions but you will have to tune it to what that means for the world you are dealing with. For a recent example of my own - a giant (Class H) out-system water discworld - the base assumption would be this is an ice-disc, with 'drier' being irrelevant here. The hotter and hottest bits may be liquid water for whatever reasons and now we can begin to get a sense of what is happening here - a big ice disc with some liquid water parts (portals to elemental fire? a core of water heated under the incredible pressure of this enormous ice-mass?) where most of the non-ice elemental life lives.

You can find some other system building resources here - Building Systems in "SpellJammer 5e" on Obsidian Portal - or Star System Creation Tables on Kulan World Journal - that can provide tables for tech levels of civilizations encountered.