Key points of M3 Hinterlands - Codex entries - Dragon Age: Inquisition
The above map presents locations, where you obtain new codex entries in The Hinterlands. Be on the lookout for various notes, letters, books and tablets. The tavern at Redcliffe deserves a separate mention.
Successive visits to the tavern unlock new codex entries connected with songs (approach the bard to receive them). It is a good idea to visit the tavern each time you are in Redcliffe.
Note - Some of the markings on the map refer to codex entries in caves and dungeons. If you cannot find an individual entry, find out if there is an entrance into an underground location around.