I don't know where you get the idea that the areas is heavily populated
I'd say it was similar to the position of Slough in the south. A smallish town in itself but surrounded by other towns and close to a large city.
A look at any map will clearly indicate it's a heavily populated area, within that Manchester/Liverpool/Preston triangle. Birmingham is havily populated but in a smaller, more concentrated area and obviously London, within the M25 is fairly well-stuffed.
I'm not saying there aren't nice, quiet, roads to cycle on (There are many within 30 mins of my old home town of Stockport and that's basically a Manchester suburb) but there's no point in arguing that it isn't a highly populated area. Within 15 miles of Wigan you have Manchester, Liverpool, Blackburn, Preston, Warrington, Skelmersdale, all considerable conurbations and probably home to 5 million people. It's the epitome of a highly populated area, it's the industrial north-west.
Onyx "Cheshire" is a tiny area around Wilmslow that actually extends north into south Manchester (Bramhall). True (more southerly) Cheshire is sparsely populated and is where the old money lives.
The South Manchester/ North Cheshire boundary has always been very elastic depending upon the snobbery of the individual resident. Stockport, Cheshire is still used by many.
My Father in Law is Wigan born and bred btw. (We had his tail docked a few year ago).