Dunno if this qualifies for bug reports or mod compat requests, but I found the reason for the map just completely ♥♥♥♥♥♥♥ up due to tiles gradually completely changing. It was being caused by Map Reroll. I'd reroll it a few times, and everything would seem fine (though the map didn't match the preview I selected) at first, but then tiles would gradually start changing once I unpaused. Usually in catastrophic ways, such as nearly all sand, or water stranding colonists. I didn't try NOT rerolling but having the mod installed, but after uninstalling map reroll, there were no more problems.

The description does say that NPS isn't compatible with mods that mess with world/map gen, so fair enough. Hopefully these incompatibilities can get ironed out eventually, though.

Other observations:

Lichen-covered dirt (defname MossyTerrain) and other biome exclusive vanilla terrain doesn't seem to have a wet variant defined.
Wet sand is intensely OP at 200% fertility, eclipsing rich soil which is 180%. Wet soil is similarly classified above rich soil at 200%.

I dried out an area of marsh and marshy soil with pumps. After a rain, all of these tiles were turned into moving water, which isn't affected by the pumps.

I tried using dev mode to turn them to shallow water and even soil, but they just start turning back into moving water, but now it happens even without rain.

I'm not sure if this is a bug or intended behaviour, but I wanted to check on it.

I'm getting spammed with this error suddenly. :/

System.Collections.Generic.KeyNotFoundException: The given key was not present in the dictionary.
at System.Collections.Generic.Dictionary`2[Verse.IntVec3,TKKN_NPS.cellData].get_Item (IntVec3 key) [0x00000] in <filename unknown>:0
at TKKN_NPS.Watcher.checkIfCold (IntVec3 c) [0x00000] in <filename unknown>:0
at TKKN_NPS.Watcher.checkPawns () [0x00000] in <filename unknown>:0
at TKKN_NPS.Watcher.MapComponentTick () [0x00000] in <filename unknown>:0
at Verse.MapComponentUtility.MapComponentTick (Verse.Map map) [0x00000] in <filename unknown>:0
Verse.Log:Error(String)
Verse.MapComponentUtility:MapComponentTick(Map)
Verse.Map:MapPostTick()
Verse.TickManager:DoSingleTick()
Verse.TickManager:TickManagerUpdate()
Verse.Game:UpdatePlay()
Verse.Root_Play:Update()

so my redwood forest is turning into a desert flats

Well redwood don't regrow. For now I use the console to spawn the few in my base again as they sometimes just disappear (and the hitbox of them is massive, so 2 blocks away is the nearest for a growing area or they chop down the tree)

so im on a Volcanic Fields map. the steam vents pop up under walls and mountain rock

Looks like I've lost my run this time. Following error is a run killer...:

System.IndexOutOfRangeException: Array index is out of range.
at Verse.TerrainGrid.TerrainAt (IntVec3 c) [0x00000] in <filename unknown>:0
at Verse.GridsUtility.GetTerrain (IntVec3 c, Verse.Map map) [0x00000] in <filename unknown>:0
at TKKN_NPS.cellData.get_currentTerrain () [0x00000] in <filename unknown>:0
at TKKN_NPS.cellData.setTerrain (System.String type) [0x00000] in <filename unknown>:0
at TKKN_NPS.Watcher.doCellEnvironment (IntVec3 c) [0x00000] in <filename unknown>:0
at TKKN_NPS.Watcher.checkRandomTerrain () [0x00000] in <filename unknown>:0
at TKKN_NPS.Watcher.MapComponentTick () [0x00000] in <filename unknown>:0
at Verse.MapComponentUtility.MapComponentTick (Verse.Map map) [0x00000] in <filename unknown>:0
Verse.Log:Error(String)
Verse.MapComponentUtility:MapComponentTick(Map)
Verse.Map:MapPostTick()
Verse.TickManager:DoSingleTick()
Verse.TickManager:TickManagerUpdate()
Verse.Game:UpdatePlay()
Verse.Root_Play:Update()

I'm getting the same error as Sakujo and a few other people in the comments. It seems to be occuring every tick. When my game runs for long enough, it can produce an output log nearly 2 million lines long. It actually crashes notepad when I try to open it. I think it's related to being on a shore tile. I'm also having an issue where the tides don't work.
EDIT: Interestingly enough, if I turn the main weather control off, but leave everything else on, I get the same error, but it happens much less frequently.

Just got a manhunter pack of giant snails, which was better than the last two of tortoises, and I checked on them only to find out they're all...
http://puu.sh/yUUuA/a959404741.jpg
Pain NaN%

Originally posted by lionsilverwolf:

Just got a manhunter pack of giant snails, which was better than the last two of tortoises, and I checked on them only to find out they're all...
http://puu.sh/yUUuA/a959404741.jpg
Pain NaN%

Oh yeah! I had the same thing, except I kept on getting raiders using them as mounts, until I blacklisted them. I don't care how bored you are, no one should ever ride a giant snail into battle.

The shores like to totally dry out

I noticed if you switch saves from a game with a different biome the scripts from the previous keep running so this ended up with my redwood forest at 60 dgrs fahrenheit turning it an ice sheet.

I'm having an issue where with a map generated even after the option was toggled off, I am still getting Lava Eruptions outside of Lava fields.

Dust storms are making my arid shrubland's creek flow. That kind of seems like the opposite the intended effect.

Originally posted by Figgis:

Looks like I've lost my run this time. Following error is a run killer...:

System.IndexOutOfRangeException: Array index is out of range.
at Verse.TerrainGrid.TerrainAt (IntVec3 c) [0x00000] in <filename unknown>:0
at Verse.GridsUtility.GetTerrain (IntVec3 c, Verse.Map map) [0x00000] in <filename unknown>:0
at TKKN_NPS.cellData.get_currentTerrain () [0x00000] in <filename unknown>:0
at TKKN_NPS.cellData.setTerrain (System.String type) [0x00000] in <filename unknown>:0
at TKKN_NPS.Watcher.doCellEnvironment (IntVec3 c) [0x00000] in <filename unknown>:0
at TKKN_NPS.Watcher.checkRandomTerrain () [0x00000] in <filename unknown>:0
at TKKN_NPS.Watcher.MapComponentTick () [0x00000] in <filename unknown>:0
at Verse.MapComponentUtility.MapComponentTick (Verse.Map map) [0x00000] in <filename unknown>:0
Verse.Log:Error(String)
Verse.MapComponentUtility:MapComponentTick(Map)
Verse.Map:MapPostTick()
Verse.TickManager:DoSingleTick()
Verse.TickManager:TickManagerUpdate()
Verse.Game:UpdatePlay()
Verse.Root_Play:Update()

I am also getting this error.