The highest points in the principal areas of both Torfaen and Rhondda Cynon Taf are not summits but locations high on hills, the summits of which are just west of the boundary in neighbouring principal areas. The highest points of the principal areas of Merthyr Tydfil and Caerphilly are not summits either but two locations near to each other on the southern slopes of a higher hill, Cefn yr Ystrad whose summit lies in the adjacent area of Powys.