I mention this every lore-thread but, portals are insanely dangerous. So much so that the Kirin Tor regulate their use and it’s the most volatile form of magic that isn’t actually banned. The ingame book " Thinking with Portals - A Memorandum on Proper Portal Usage" has all the lore you’ll need on it and I won’t parrot it word for word here, but! The most import thing to know about portals is this:
Rule #1: Do not create a portal to anywhere but the designated Kirin Tor portal drop-off zones. The most dangerous aspect of the portal spell is its vast potential. We realize it’s easy for a mage to create a door to anywhere, so our only way to combat such potentially deadly acts is to make it punishable by death.
Special Issue License D-6 permits open portal usage, but is rarely issued. Speak with your local Portal Trainer about qualifying for this license.
Making portals to anywhere but the designated spots you see ingame is punishable by death.