Like one area, this large region (4)
I believe the answer is:
asia
'this large region' is the definition.
'asia' can be an answer for 'region' (I have seen 'populous region' mean 'asia' so perhaps 'region' could also mean 'asia'). I'm unsure of the 'this large' bit.
'like one area' is the wordplay.
'like' becomes 'as'.
'one' becomes 'i' (Roman numeral).
'area' becomes 'a' (maths abbreviation).
'as'+'i'+'a'='ASIA'
Can you help me to learn more?
(Other definitions for asia that I've seen before include "Large area" , "Thailand and its location" , "Tigers found here" , "Eastern continent" , "Great continent" .)