I lived in the Ruhr for a while, and I have to say that I think that it is quite easily overlooked, but nevertheless true: the Ruhr <i>is</i> a mega-city.  What once were unique enclaves and villages and small towns are mere pit-stops across a vast concrete jungle, which has - admittedly - quite some green spaces between it, but is nevertheless well-navigated by its citizens.  It is nothing to go for a night out from Bochum to Mannheim-Ruhr, or live in Dusseldorf but work in Cologne .. the rail - and general design of German civilization itself - allows for a much, much bigger scale of things - in this region - than might be generally accepted.<p>I think of the Ruhr region as a mega-city-one (Judge Dredd) kind of thing, anyway ..