Pern is a big place, and the playable locations in TPA are only a small part of it.
The Northern Continent
Map from The Atlas of Pern
The World
Map by Todd McCaffrey
The Northern continent is a relatively small landmass in the grand scheme of things, but other than a tiny portion of the south it's all that TPA Pernese folk know about. Semaca is located along the river on the far western extreme of the map; clearly, the people who have made it there are a long, long way from home.