Here are a couple of maps of the One Piece world. In no way am I claiming these are correct – I don’t think Oda has drawn one and I personally don’t think that we’ll ever see one in canon until Nami finishes hers 🙂
The first one is a Japanese version (I’ll try to find a translated version) first posted by dflamunmyob @ reddit.
The second one was originally posted by Knightmare_X @ reddit.
Both images are clickable to imgur.