I made general observations and counted tiles using the map search feature to get an idea of the percentage change. This is a total speculation based on a small number of tests. I do not have any knowledge of the algorithms and math involved. My observations are based on duel Pangea, standard continents and huge continents and islands maps.
I ran the same seed map with different settings. It allowed me to compare the original map to the adjusted map with the new settings. I found that a duel size pangea type map fits well on the screen for demonstration purposes with all of the landmass visible along with the features. So let’s look at the first setting.
Temperature settings impact terrain generation, specifically the number of Desert, Tundra and Snow tiles.
Cold map produces more tundra and snow tiles AND less desert.
It is pretty obvious, isnt it. A lot of tundra is added, specifically 170%. According to my observations with other map types and sizes, the increase n tundra tiles could range from 100 to 250%. I guess it depends on the initial configuration.
The snow tiles number added is 0 in most cases. But you can tell the polar caps are heavier for sure so there is more ice.
Desert is almost eliminated. We went from about 70 to 6 tiles. I have seen a reduction in desert tiles go anywhere from about 70% to 90%.
I will speculate that if there is less increase in tundra tiles, then there will be a higher reduction in desert tiles to bring the ratio to a certain balance.
Cold map seems to reduce the number of flood plains tiles as well. Makes sense, as desert flood plains are gone.
It’s interesting that the rivers are different, as well as the Lakes and Natural wonders
Temperature – Hot
More desert less tundra. So expect the desert size to double in size. And Tundra and snow tiles reduced by 40-70%.
Hot map also creates slightly more floodplains.
Rainfall settings impact feature generation, specifically the number of Woods, Rainforest and Marsh tiles. This setting provided the most consistent numbers across various tests.
Arid (rivers lakes the same)
This map produces less Woods Rainforests Marshes.
Because it was consistent I can state that you would get ⅔ less marches, about ⅕ less woods, and some rainforest would be removed, only around 10%.
This setting is a polar opposite and has similar numbers in reverse. You get ⅔ more marshes, ⅕ more woods and some 10% more rainforest tiles. I always assumed that higher rainfall would provide more rainforest rather than woods, so this was the most surprising result for me personally. I think wet and cold combination can built a yields porn heaven for the lady of the reeds fans.
World Age settings impact terrain generation, specifically the number of Hill, Mountain and Volcano tiles.
New World (rivers, lakes)
New age maps get the number of Hills boosted, but it seems to vary and can range quite widely between 25%-75%. But civs like Gaul can certainly benefit from it.
I found that the New age does not grow mountains much, maybe 10% and in some cases it produced less mountains, which is really odd and in contradiction to the description that says more mountains.
It does add plenty of volcanoes though usually by at least half or sometimes even double the number. Geothermals thought are completely unaffected, if you were wondering. It’s not wrong to assume that we would have more geothermals, but it is not the case.
But what’s interesting, because there are less flat tiles, the number of flood plains falls. And another side effect is the average reduction of desert and tundra tiles by about 25-30% making the New Worl climate more temperate.
Flattens the hills for the most part. You can lose as much as a quarter. It sort of opens up the map a bit. But funny enough on this map the number of hills stayed the same, larger size maps have a bigger impact.
Another weird part is that you get more mountains, not less. Here we have 16 as opposed to 11 originally and 13 with the new age. In other tests I got about 10% more mountains as well, not less. Overall, I saw more mountains in the Old Age maps than the New Age maps.
Old World also seems to grow the number of Floodplain tiles, perhaps because it is a bit flatter overall.
Sea Level settings impact the ratio between land and water tiles. Sounds pretty straight forward. However, I would assume it would be like by a third, but that is not the case.
High Sea level reduces the size of the total landmass.
Higher water levels around the continent shrinks it a little bit just by 7-12% depending on the amp. But not enough to create the water passageways around the polar caps though. Too bad. If you do want to have no ice adjacent to the land then use Not Your Map pack mod, it has a map setting that allows you to remove it.
Low Sea level increases the size of the total landmass
Obviously the opposite effect, less water and more landmass by similar rate – only 10% on average.
The weirdest part that I have observed happens to non-pangea maps like Continents. It looked like the same map seed produced a new land distribution. The high and low sea level maps look completely different from the original. Sometimes it’s not even close.