Replace hardcoded z-level numbers with a trait system

code/modules/mapping/space_management/zlevel_manager.dm

@@ -0,0 +1,32 @@
+// Populate the space level list and prepare space transitions
+/datum/controller/subsystem/mapping/proc/InitializeDefaultZLevels()
+	if (z_list)  // subsystem/Recover or badminnery, no need
+		return
+
+	z_list = list()
+	var/list/default_map_traits = DEFAULT_MAP_TRAITS
+
+	if (default_map_traits.len != world.maxz)
+		WARNING("More or less map attributes pre-defined ([default_map_traits.len]) than existent z-levels ([world.maxz]). Ignoring the larger.")
+		if (default_map_traits.len > world.maxz)
+			default_map_traits.Cut(world.maxz + 1)
+
+	for (var/I in 1 to default_map_traits.len)
+		var/list/features = default_map_traits[I]
+		var/datum/space_level/S = new(I, features[DL_NAME], features[DL_LINKAGE], features[DL_TRAITS])
+		z_list += S
+
+/datum/controller/subsystem/mapping/proc/add_new_zlevel(name, linkage = SELFLOOPING, traits = list(), z_type = /datum/space_level)
+	var/new_z = z_list.len + 1
+	if (world.maxz < new_z)
+		++world.maxz
+		CHECK_TICK
+	// TODO: sleep here if the Z level needs to be cleared
+	var/datum/space_level/S = new z_type(new_z, name, linkage, traits)
+	z_list += S
+	return new_z
+
+/datum/controller/subsystem/mapping/proc/get_level(z)
+	. = z_list[z]
+	if (!.)
+		CRASH("Unmanaged z-level: '[z]'")