Fun idea. It's not just an issue of DL, it's an obstacle of 2D top-down mapping in general. Even pencil-and-graph-paper mapping struggles with how to represent an underpass / overpass situation (it's usually a dashed-line - - - - - representing the underpass). The problem being similar in paper or digital mapping, same with DL, when PC's pass over the underpass they are going to see it exists (even when it might actually be a totally disconnected subway tunnel). And then there's the corollary problem when the PC's travel the underpass road, they run into the appearance of walking over the walls of the overpass. The whole problem is even worse if they have an encounter (monsters) in the criss-cross area. API script to handle this: Don't know of one, what's the vision for how that would work anyway? I guess it would flip-flop the Z-order of the floor/wall-tile and toggle block/unblock of the corridors of overpass/underpass alternately. Manual ways of handling it by-hand during-gameplay (Granted this slows down gameplay) --- 2 things normally have to change, the Dynamic Light blockades and the underlying floor-tunnel-hallway graphic that has walls. SPECIAL NOTE: If you construct your dungeon entirely out of DL walls with background-page-color, no battlemap or wall tile set, then this whole process would be easier, you would only need to contend with switching the DL. But yeah, assuming you need to switch the "z-order" of the floor-wall-tiles (Bring To Front --- while this will wrongfully appear to the GM as creating an overpass, it is effectively revealing the underpass for purposes and perspective of the players/PC's), and then switch the DL walls (unblock the east-west underpass, block off the north-south overpass). Workaround method that I personally use --- maybe unconventional but I sometimes do Sub-Levels "off to the side" in my Map Page of Roll20. Sometimes I even construct a "chutes-and-ladders style" DL pathway that leads (long walk distance) to another wing of the map where the sub-level is represented. I just tell the players "Walk your token waaaay down that tunnel to the left, it's not really that far, it just represents the ladder/stairs you climbed to get into the sub-level / underpass area." This works more for side-rooms / basements / cellar / attic, doesn't work so great for warrens with dozens of underpasses or even triple-quadruple subway layers. Side-view map is another alternative to consider. Like a cutaway-map. Unfortunately we sacrifice seeing your PC's side-by-side in depth (Y-axis) in the rooms, but it's great for mapping elevation changes (z-axis). Looking forward to see what you come up with.