Taleworlds created the campaign map for Calradia in the external software package Houdini. This feeds into the game via a worldmap tileset, which is not editable by modders. IIRC the terrain for Sandbox\Main_map has been white in the Scene Editor (ok in game) since 1.8.0 or just before. If you want to edit the terrain of Calradia, you should go to the property browser and under the vista textures box change the tileset from worldmap to none - this disables the Houdini tileset. However, doing so will also disable the vista texture in that tileset which colours terrain in game, so you will need to supply your own 16K vista and normalmaps. IIRC editing the terrain without disabling the tilset will cause a crash on saving the campaign map. Also, unless there were undisclosed changes in 1.9.0 saving your map as Main_map to your own mod will destroy its terrain paint layers due to hardcoded optimisations - most modders save their campaign maps as modded_main_map and use Aurelian's MapFix to avoid this and other hardcoded issues such as main_map_physics_heightmap. Taleworlds have been looking into these problems for some time but I doubt they will be resolved this side of release.
BTW most modders just remove Calradia's terrain and start from scratch building entirely different custom campaign maps.
PS if you are not editing terrain, it may be possible to just relocate settlements. In such a case, take care to detach them from their current campaign_icon_capsule and parent then to a campaign_icon_capsule appropriate to their new location.