I want to talk about the visibility set method used in our game Pergamon. We are making a Metroidvania. In 2d, this problem is hardly a problem at all. The world is divided into rooms – when the player goes through a door, you load the neighboring room, unload the current one, done. Some game briefly have both loaded at once. Others, like Super Metroid, only show you the door during a brief animation to cover up any time spent destroying the old room or preparing the new one. On a modern system, on a 2d game like Super Metroid, there’s really no reason you can’t have huge chunks of the world loaded at once.

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