What's funny with that map is there are areas on the map which English language (nevermind the Mancunian accent) isn't the first language of the area yet places which aren't considered a part of MCR (such as Heywood) which is under Rochdale council has plenty of people living there with strong Mancunian accents and routes from the MCR overspill of yesteryear.
People with ancestry routes dating back hundreds of years in MCR find themselves occupying areas such as Heywood and North Bury yet I go into MCR centre and a lot of people these days have either Southern accents or don't even speak English.
Only true Manc accent in our football team is from Pablo Zabaleta (and he's Argentinian)