Border is quiet at this place, one of two in the world (10)
I believe the answer is:
hemisphere
'one of two in the world' is the definition.
(eg northern and southern hemisphere)
'border is quiet at this place' is the wordplay.
'border' becomes 'hem' (I've seen this before).
'quiet' becomes 'p' (music symbol for 'piano', ie soft or quiet).
'at this place' becomes 'here' (synonyms).
'hem'+'is'+'p'+'here'='HEMISPHERE'
(Other definitions for hemisphere that I've seen before include "covers half the world" , "Half the globe" , "part of the world" , "Half of the earth" , "Global division" .)