Well I can say I come from a unique city when it comes to accents. Scouse, geordie, cockney, all accents from around the country are spoken across an area. Like all of Tyneside speak with the geordie accent, same for the Fylde peninsula area having the scouse accent, the midlands everyone talks like Ozzy Osbourne etc etc.
I come from Hull and the accent there although sounding awful when compared to some others, is only spoken within the city. Travel up the road to Beverley just 5 miles outside of the city boundary and they have quite a cultured accent compared to my home town. Its unique in not spreading from the city, some would say that this is a good thing when hearing it