cartographers and mermaids

[Blue Mythril]

Hey guys, very long time no see!
Was wondering whether someone could help me find a very random fantasy book, that involved four female cartographers and featured mermaids? I know this is very little info, my friend and I were talking about it, but we both read it over ten years ago now and haven't the foggiest what it's called or who it's by!

Any help would be sweet.

 

[K. Riehl]

Perhaps The Steerswoman by Rosemary Kirstein? I remember that it is about female cartographers but I don't remember the mermaids.