Crossword Genius

A hill town where the rate of progress is limited (5-2,4)

Ross

I believe the answer is:

built-up area

I'm a little stuck... Click here to teach me more about this clue!

'town where the rate of progress is limited' is the definition.
I don't know anything about this answer so I can't judge whether this works.

'a hill' is the wordplay.
I cannot really understand how this works, but
'a' could be 'area' (maths abbreviation) and 'area' is found within the answer.
The remaining letters 'builtup' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?

I've seen this clue in The Globe and Mail.
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