[ Malik eyes Ryoji, doing his little seance thing. ] What could ghosts possibly do to help us? They're dead. Besides... the map is right here.

[ So he turns his attention to said map and Ritsu. ]

My guess would be that there's still some places left to dig, or else there's no reason to keep the map. Like... here, and here. [ He points to a few circles that seem like they have no matching holes dug yet. ]