The most common and most likely answer to this crossword clue is the 11 letter word GEOMETRICAL
I've seen this crossword clue in Independent
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Buddy explains!

The straight part
We know that "covering points and surfaces?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case covering points and surfaces? = geometrical.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 GEOMETRICAL mean?
GEOMETRICAL adjective- Of, or relating to geometry; geometric.
- (of a design) Consisting of lines and simple shapes.
- (of a staircase) Having the stairs supported by the wall at one end only.