The most common and most likely answer to this crossword clue is the 9 letter word TOWNSCAPE
I've seen this crossword clue in The Times
T
O
W
N
S
C
A
P
E
More clues leading to the result TOWNSCAPE
Buddy explains!

The straight part
We know that "sight of built-up area" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case sight of built-up area = townscape.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does TOWNSCAPE mean?
TOWNSCAPE noun- A view of a town, or a subjective image of a town
- A depiction of an urban scene
- To design and lay out (buildings) as a town.