two more PRs.

code/modules/mapping/map_template.dm

@@ -84,6 +84,13 @@
 	if(T.y+height > world.maxy)
 		return
 
+	var/list/border = block(locate(max(T.x-1, 1),			max(T.y-1, 1),			 T.z),
+							locate(min(T.x+width+1, world.maxx),	min(T.y+height+1, world.maxy), T.z))
+	for(var/L in border)
+		var/turf/turf_to_disable = L
+		SSair.remove_from_active(turf_to_disable) //stop processing turfs along the border to prevent runtimes, we return it in initTemplateBounds()
+		turf_to_disable.atmos_adjacent_turfs?.Cut()
+
 	// Accept cached maps, but don't save them automatically - we don't want
 	// ruins clogging up memory for the whole round.
 	var/datum/parsed_map/parsed = cached_map || new(file(mappath))

code/modules/mapping/mapping_helpers.dm

@@ -18,7 +18,7 @@
 
 /obj/effect/baseturf_helper/LateInitialize()
 	if(!baseturf_to_replace)
-		baseturf_to_replace = typecacheof(/turf/open/space)
+		baseturf_to_replace = typecacheof(list(/turf/open/space,/turf/baseturf_bottom))
 	else if(!length(baseturf_to_replace))
 		baseturf_to_replace = list(baseturf_to_replace = TRUE)
 	else if(baseturf_to_replace[baseturf_to_replace[1]] != TRUE) // It's not associative