Thank you so much for this, you've been incredibly helpful. I've been following along with the document and mostly everything has been going smoothly. One part I'm having a bit of difficulty with is the settlements section. I'd like to rearrange all the floating towns and castles, but I didn't see anywhere in physics to disable terrain snapping, and some villages are attached to parent towns. Is there any easy way to simply grab one whole town or village and align it where I want to?
Recent patches reorganised settlements into campaign icon capsules and added Town Entity Manager scripts to each settlement. They were added to Main_map to improve performance via faster hierarchical culling of objects/icons not in view. I'm advised they will only function this way after they are registered and we will need to wait for documentation for that process. In any event, such capsules need to contain settlements in proximity to each other, so, the organisation in Main_map wouldn't work on an alternative worldmap where settlements are differently distributed. Accordingly, for now, I've deleted all the campaign icon capsules (by editing the scene.xscene file - don't do it in the editor or you'll lose all their children unless you detach them first) as they clutter up the entity search panel in the scene editor.
That said, settlement placement on a new worldmap is a grind. Terrain snapping is enabled on some settlement components and not others. Mainly because it works sometimes and is a problem in other instances. Bannerlord's settlements have been customised to the terrain contours at their location in Calradia. This won't match yours.
For Towns/Castles:
Select the whole entity (i.e. town_K1) in the editor's entity search panel. Then use the editors transform widget to move it into approximately the correct position. Ensure the x and y rotations remain zero as slanting a town generally looks bad and doesn't resolve underlying component misalignments. I prefer to do this using the level 3 fortification icons, but each fortification level needs to be customised to your terrain.
Gatehouses are a problem. They generally mount siege engines and banner positions and are often flanked by wall breach sets. So, best to get the front as best vertically aligned as possible to minimise changes there. Equally, you need to check the attacking siege engines and volume boxes sit on passible navmesh and are correctly snapping to your new terrain.
Next for each level in turn, check and realign heights of walls/towers/etc. to ensure they're grounded or stagger reasonably up or down slopes. Make sure siege engines and banner positions volume boxes are moved with the related meshes. For example shift click lets you select an individual tower then shift control click lets you select a second item to be moved with it. You can group several items this way to move them in concert. Be careful with this as keyboard slips can spawn unwanted duplicate entities.
Houses etc. inside towns were treated differently by different Devs. Most set them up as a parent child group separate from fortification levels allowing you to place them once. However, other Devs place them inside fortification levels requiring you to redo it each level. Most houses can just be snapped to terrain using that house's visibility flags. You can select all the same type of house in the editors search panel together and collectively set their flags. However, be careful, some particularly Aserai houses are stacked for terraced visuals or markets/arenas may be mounted on platforms, which will be destroyed by terrain snapping.
Obviously, there's lots of other stuff to customise such as adding walls to the backs of towns that were backed by a mountain/river/sea in Calradia etc.
For villages:
Unlike towns, the core village icons are single composite meshes, which can't be individually customised. Accordingly, they need to be rotated/slanted into the terrain. Just focus on getting the level 3 buildings as well grounded as possible. Then check the other levels. Next, select all the production icons (you need to be in level 3 to see them all - even here some may be underground) and set their positions and snapping flags to suit your terrain.
I hope that helps. Unfortunately, learning is a trial and error grind.