There have been a few indications that Far Cry Primal uses a modified version of the map from Far Cry 4, so we decided to compare both games side-by-side, visiting the same locations on the map. After having made the comparison it seems safe to say that yes, the Oros map from Far Cry Primal recycles plenty from Far Cry 4's Kyrat.
The basic layouts and architecture are very similar, but the two maps feel very different. Kyrat seemed considerably bigger than Oros, and some areas were heavily modified. It's not a mere paint job, but a complete revamp of the map, and although underneath there are similar parts, the experience of exploring the two places is completely different.
You can see the similarities and differences for yourselves in the screens below.
Far Cry 4/ Far Cry Primal