So, if it's not strictly written
Korrect what is and what isn't in an area (now known as areaX), how about just calling areaX something that you wont find on a map, but you will know where it is...
How about
ThatbuiltupareacoveringbothRheinandRuhrareasbasicallyanywherethatHagenlotwouldco
nsidertravellingforanightoutonthepiss? phew

Bit of a mouthful I know, I suppose we could even call it something sensible like... The Ruhrpott... or even AreaX or even better... leave it like it is.