commander_in_terrain_specialisation

commander_in_terrain_specialisation = {
	OR = {
		AND = {
			has_trait = desert_warrior
			location = {
				terrain = desert
				terrain = desert_mountains
			}
		}
		AND = {
			has_trait = jungle_stalker
			location = { terrain = jungle }
		}
		AND = {
			has_trait = open_terrain_expert
			location = {
				terrain = farmlands
				terrain = plains
				terrain = steppe
			}
		}
		AND = {
			has_trait = rough_terrain_expert
			location = {
				terrain = hills
				terrain = mountains
				terrain = wetlands
			}
		}
		AND = {
			has_trait = forest_fighter
			location = {
				terrain = forest
				terrain = taiga
			}
		}
	}
}

As written in game/common/scripted_triggers/00_commander_triggers.txt.