Altitudo

Altitudo raises the ceiling and lowers the floor of the Overworld and the Nether, and
makes what generates there follow them. The Overworld runs from -2032 to 2031 and the
Nether from -128 to 1023 — as deep and as tall as a Minecraft world is allowed to be.

It is a world type. Pick Altitudo on the world creation screen and you get the tall
world; leave it alone and you get exactly the vanilla one, in the same instance, with no
setting to remember. Nothing under minecraft: is replaced, so worlds you already have
are untouched and other data packs keep working.

The Overworld

Thirty times the depth, and it is cave the whole way down rather than a taller block of
stone. The bounds that decide where caves may exist come with the floor, and so do the
aquifers that decide whether a cavity is dry, a pool or flooded — so the deep has open
systems, water, and lava that is there because something chose it rather than because the
game gave up.

The Nether

Eight times the generated height, with the bedrock roof rising to meet it and the same
128 blocks of building space left above it that vanilla leaves. The lava sea gets as deep
as the floor is low: 160 blocks instead of 32.

The Nether is the half most mods of this kind leave out. Raising only the build limit
gives you somewhere to put blocks on top of the lid; raising the generation without
moving the density gradients with it fills everything above the old roof with solid
netherrack. Altitudo moves both.

Ore, and other mods’ ore

Vanilla writes where ore may appear as a height, and most of those heights are absolute.
A world that is thirty times deeper does not move them, so the space it gained would be
bare stone — the quiet kind of failure, where nothing reports an error and you only find
out by digging through it.

Altitudo emits vanilla’s own placement unchanged and adds copies of it further down,
so density cannot fall below what vanilla had, at any depth. Below sea level it rises
with depth, to 4.5× vanilla at the floor by default, on a curve you can set.

Other mods’ ores travel with it. An ore is recognised by being configured as one, not by
a list of ids, so nothing has to be named and nothing has to be updated when you add a
mod. A mod that would rather be left alone says so with a single data pack tag.

Under it

The dimensions are computed, not shipped. One setting gives the extent, and the files the
game reads are built from it in memory — so any depth is a value rather than one of a
handful of prebuilt data packs, and vanilla’s own worldgen files are read and adjusted
rather than copied and left to go stale a version later.

Reading the two vanilla dimensions side by side, they are one formula: the box is the
generated height plus a roof gap, and logical_height is the generated height. The Nether
is not a different shape, it is the same shape with a gap above the roof. Altitudo says
that directly, which is also why portals still land on the ground rather than in the lava
sea.

Every rewrite is counted and checked. A transform that matches nothing still produces
valid JSON and a world that generates, so "found no match" is an error that stops the
world screen from opening — not a quiet pass-through that hands you a world with no caves
in it.

Requirements

NeoForge 21.1.x on Minecraft 1.21.1. MIT licensed.