Help remembering book title

Its one of those things my brain has died I think. I am sure the book
I'm looking for was recommended by someone on this list when I asked
what people were reading.

All I specifically remember is a scene where a middy or trainee of some
sort on a ship is given a task by their OCTO that involves finding their
way around and possibly updating an innacurate map cube. That the maps
the ship handed out were leading to closed off areas or something.

but for the life of me I can't remember the author or the name of the
book. My memory is that both the trainee and the OCTO are female though
if that helps?

its like the song that never ends, I can't get it out of my brain

thanks
Flute