Insignificant place that could be nowhere? Not so (3-5,4)

I believe the answer is:

one-horse town

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'insignificant place' is the definition.
'one horse town' can be an answer for 'place' (I have seen 'Poor place' mean 'one horse town' so perhaps 'place' could also mean 'one horse town'). I am not certain of the 'insignificant' bit.

'could be nowhere? not so' is the wordplay.
'could be' indicates anagramming the letters.
'nowhere'+'not'+'so'='nowherenotso'
'nowherenotso' anagrammed gives 'ONE-HORSE TOWN'.

'that' is the link.

Can you help me to learn more?

I've seen this clue in The Guardian.

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