So far, the characters have been grouped based on a theme.
(Both are even lined up with Kaido and Linlin respectively)
Dressrosa Allies (Law, Barto, Corazon)
Warlords (At least partly)
This could help us determine how Oda places the others. I imagine all the Marines get boxed together, Straw Hats are a given, and Shanks and Teach occupy similar spots as Linlin and Kaido, looming at the corners of the mural.