Sectional development by the sea (9)

I believe the answer is:

coastline

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'the sea' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how one could define the other.

'sectional development' is the wordplay.
'development' indicates an anagram.
'sectional' anagrammed gives 'COASTLINE'.

'by' acts as a link.

Can you help me to learn more?

(Other definitions for coastline that I've seen before include "Shape of the seashore" , "Outline of land from sea" , "21 [SEASIDE]" , "Where the sea meets the shore" , "Shore boundary" .)

I've seen this clue in The Daily Express.

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