Region in Matsuida oddly ignored (4)
I believe the answer is:
asia
'region' is the definition.
(I have seen 'populous region' mean 'asia' so perhaps 'region' could also mean 'asia')
'matsuida oddly ignored' is the wordplay.
'oddly ignored' indicates alternate letters.
The alternating letters of 'matsuida' are 'ASIA'.
'in' is the link.
(Other definitions for asia that I've seen before include "Part of the world" , "Populous continent" , "The Orient" , "Continent bordering three oceans" , "huge region" .)