Newbie questions

Can someone explain few basics to me, pls?

1) People mention doing T16+ maps. Do they mean T16 and T17, or one can get even higher? I know you can corrupt map to make it T16 and then open it on irradiated node. Is it maximum?

2) When you instill waystones with delirium it says something like 'Players are % delirious'. What exactly this buff/debuff means?

3) Where do people get gems above level 18? Best I could get was level 18 at T15-T16 maps.

The tiers of maps are just depending the level of the zone, T16s you can get by corrupting a T15. And Irradiated and Corrupted zones give +1 level each, if you get all 3 things you are running a T18.

The Delirium scaling right now is unknown, at least the wiki says that, but if it works like the first game it means that every 20% monsters deal increased damage and take less damage. In the first game the maximum was 100% delirious, but in the Simulacrums in PoE 2 you can get up to 140%.
The amount of damage dealt and taken that the monsters get in the first game are not official and are just estimates, but the community is pretty accurate usually.

And the gems just drop, they are high rarity drops. At zone level 82 if a gem drops you have 79% chance for it to be 18, 19.8% for it to be 19 and 1.2% for it to be 20. And the higher you go with the zone level the more chances you get fro 19s and 20s and less for 18s.

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Vic5Vicious#7214 wrote:

The tiers of maps are just depending the level of the zone, T16s you can get by corrupting a T15. And Irradiated and Corrupted zones give +1 level each, if you get all 3 things you are running a T18.

And the gems just drop, they are high rarity drops. At zone level 82 if a gem drops you have 79% chance for it to be 18, 19.8% for it to be 19 and 1.2% for it to be 20. And the higher you go with the zone level the more chances you get fro 19s and 20s and less for 18s.

Thank you for explanation!
Though, what do you mean by 'the higher you go'? Isn't level 82(which equivals T18?) a maximum possible level of area?

Also, what does 'Difficulty' term means? I saw +levels of difficulty on atlas map, but there was no real explanation on details. Does it simply mean +level? Like uhh.. level 80 map with level 83 boss on it, something like that?