Its cities are Manchester and Salford and its large towns are Oldham , Bury ( city ) , Rochdale , Ashton-Under-Lyne , Stockport , Wigan and Bolton . It encompasses one of the largest metropolitan areas in the United Kingdom and comprises ten metropolitan boroughs : Bolton , Bury , Oldham , Rochdale , Stockport , Tameside , Trafford , Wigan , and the cities of Manchester and Salford .