one of the appearances that open space tiles add as vis_contents was an unchanging grey cover. its useless to keep it as vis_contents since its not supposed to change so its better to have it as an overlay. its possible that i can make openspace tiles not add the turf below as vis_contents and instead listen to objects entering and leaving it with connect_loc and add those objects as vis_contents then but that sounds like more trouble than its worth
edit: probably not the last part
overlays < vis_contents in maptick cost
also tramstation has the most open space tiles in high traffic areas compared to other maps. openspace tiles have 2 vis_contents each, equivalent to 2 objects that sendmaps processes every tick this pr only makes it 1 appearance in vis_contents. its also the map with the current highest maptick per player according to lemons graphs
