Once a redeveloped area on the map (5)
I believe the answer is:
ocean
'area on the map' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.
'once a redeveloped' is the wordplay.
'redeveloped' indicates an anagram.
'once'+'a'='oncea'
'oncea' is an anagram of 'OCEAN'.
Can you help me to learn more?
(Other definitions for ocean that I've seen before include "One of the Seven Seas" , "A lot of water!" , "Big sea" , "Indian, for example" , "Large stretch of water" .)