Description:
This is not a complete world map. Rather, I've taken the Volturnus Regional Map and stuck it in a geodesic triangle, which would show a larger territory. As you'll note, the player's map is really hard to see in the field of white.

In other words, much of Volturnus was never revealed to the players or the referee.

What we do know comes from the game:

"Volturnus is a hot, dry world with many types of hostile terrain. The endless deserts, rugged mountains, volcanic wastes, and dangerous salt flats are constantly scoured by a strong southwesterly wind. Despite these harsh conditions, rare patches of forest and even a few lakes have managed to maintain a perilous existence..."