(counties of Shropshire and Herefordshire ); and to the south by Rhondda Cynon Taff , Merthyr Tydfil , Caerphilly (county borough) , Blaenau Gwent , Monmouthshire and Neath Port Talbot . Most of Powys is mountainous, with north-south transportation by car being difficult. The majority of the Powys population is made