byond - Modules - Types

code/_onclick/hud/map_popups.dm

/atom/movable/screenA screen object, which acts as a container for turfs and other things you want to show on the map, which you usually attach to "vis_contents".
/atom/movable/screen/map_viewA screen object, which acts as a container for turfs and other things you want to show on the map, which you usually attach to "vis_contents".
/atom/movable/screen/backgroundA generic background object. It is also implicitly used to allocate a rectangle on the map, which will be used for auto-scaling the map.