It seems Ubisoft might have taken advantage of the Far Cry 4 map to build the world of Far Cry Primal, according to reports from Gamepressure. Comparing the layout on Kyrat (Far Cry 4) and Oros (Far Cry Primal), it is easy to identify similarities between the two, especially when comparing bodies of water.
We can't say for sure if Ubisoft actually reused the entire map geometry, but it would not surprise us if it was the studio's starting point. Many developers re-purpose maps, mechanics, textures and other assets to save time and resources. That said, even after spending many hours with Far Cry 4 and Far Cry Primal, we never had the feeling that Oros was a recycled version of Kyrat.
The lay of the land, foliage density, and the absence of technology, completely changed our exploration experience. If it really is the same map, Ubisoft disguised it well. Later today we intend to compare sections on both maps to get a better idea for ourselves about the differences and similarities.