Urban area: it’s found within country’s borders (4)
I believe the answer is:
city
'urban area' is the definition.
(I know that city is a type of city)
'it's found within country's borders' is the wordplay.
'found within' means one lot of letters goes inside another.
'borders' says to hollow out the word (remove centre letters) (only the edge or border letters remain).
'country' with its middle removed is 'cy'.
'it' placed inside 'cy' is 'CITY'.
(Other definitions for city that I've seen before include "Manchester, e.g." , "See 5" , "See 17" , "See 9" , "See 4" .)