This is for fully filling the map out in all 6 areas.
If you reached the end and don't have it, I'd teleport around and compare all your location maps to ones in a guide as there are a few areas where there is a connected room but the map doesn't show a line telling you there is a room there as it's meant to be secret. Either secret treasure, or in one instance a secret boss fight.
I'll provide
this steam guide as it includes finished maps you can compare to, if your map looks finished but you don't have the achievement it's likely a secret location you're missing and you will spot it while comparing maps to the ones here.
https://steamcommunity.com/sharedfiles/filedetails/?id=21896...I did not make the guide I linked. it was made by the steam user rarestMeow