Charting hills and defined summits in Africa (4)
I believe the answer is:
chad
'in africa' is the definition.
('Chad' is part of 'africa')
'charting hills and defined summits' is the wordplay.
'summits' suggests taking the first letters (I've seen 'summit' mean this (the letter at the top is the summit)).
The initial letters of 'charting hills and defined' is 'CHAD'.
(Other definitions for chad that I've seen before include "African country south of Libya" , "cartoon character" , "Punched paper; African nation" , "African country and lake" , "Large, shallow lake in north central Africa" .)