Subway Megadungeons

Here's a half-formed thought on megadungeon mapping. (albeit one that has probably already been done to death, then resurrected as a zombie thrall, turned by clerics, dispatched by adventurers, and then ground down for glue)

Need an megadungeon/underworld map quick? Use an underground map ('subway' in Western Continentalist).

• Each station marker is either a single isolated room, or a Dyson Logos/Dave's Mapper geomorph; 
• interchanges between lines are larger pre-planned clusters of levels; 
• the lines between stations are the seemingly endless tunnels, sewers, burrowings and wormholed cellars that give the undercity its intimidating scale. 
• The railway interchanges? They might be Saturday Night Specials, sealed sub-areas, or dimensional portals to other worlds entirely.

I've recently decided to expand the Vaults into a full-scale Tekumel-style underworld. Being an unabashed Englishman I've decided to use the classic London Underground map as the basis of my underworld.

Here's a spatially corrected version (created by Mark Noad) which combines the clarity of information of the classic Harry Beck schematic map with the spatial clarity of the 1930s geographic version.

The existing Vaults megadungeon will be roughly where the Bank-Monument interchange is. Lots of connections from there to as yet undefined areas underneath other parts of the Lost City of Nagoh. Some might spin off from Level 1 of the existing megadungeon, others from levels further down.

All I need to do is repurpose the exasperatingly familiar pale blue line of the River Thames as a canyon, rift, escarpment, or perhaps some sort of odd underground environmental anomaly, and Bob's yer muvva's bruvva: instant undercity ~and~ a schematic layout of the Lost City of Nagoh.

Yes, this is all very lazy DM. But I have good form for that. My world map? The Green Lantern map of Mosaic. My Sea of Os'r map? An old map of the Aegean Sea, flipped and rotated. It works for me. Less time wasted mapping = more time for play.

Pic Source: Mark Noad