How Minecraft Builds Entire Worlds from a Single Number

How Minecraft Builds Entire Worlds from a Single Number

On May 17, 2009, Minecraft showed up for the first time. Since then, it’s gotten numerous updates, new features, and over its existence for almost two decades, has still remained one of the most played games in the world. People have spent thousands of hours mining, building, and just wandering around in worlds the game generates for them.

But have you ever stopped and wondered- how does the game even make those worlds?

Procedural Generation: The Game Builds It So You Don’t Have To

Specific tiles have different procedural generation characteristics. Source:https://gpuopen.com/learn/work_graphs_mesh_nodes/work_graphs_mesh_nodes-procedural_generation/

Minecraft doesn’t have a team of designers hand placing every mountain and cave. Instead, it uses something called procedural generation. In essence, the game follows a set of rules and math to figure out what goes where.

Instead of storing every single block in memory, Minecraft stores a set of generation rules. When you walk into a new area, the game just runs those rules on the spot and builds the terrain right there.

This is how it creates:

• Terrain and elevation
• Caves and ravines
• Biomes
• Villages and structures
• Ore deposits
• Trees and vegetation

The result looks like someone carefully designed it. But it’s all just algorithms.

Seeds: One Number, One Entire World

source: https://www.chunkbase.com/apps/seed-map#seed=-7717020008708333732&platform=java_26_2&dimension=overworld&x=0&z=0&zoom=0.5

Every Minecraft world starts with a seed — just a number. That number goes into the games random number generator, and from there, the entire world gets built.

Here’s the cool part: because computers are deterministic (they always follow the same steps), the same seed will always build the exact same world. Every mountain, every cave, every village, in the exact same spot.

• Same seed → Same world
• Different seed → Different world

Think of the seed like a world’s DNA. Everything that world will ever be is encoded in that one number.

But How Does One Number Create All That?

Computers can’t actually generate truly random numbers. What they do instead is fake it, using something called a pseudo-random number generator (PRNG).

One of the simplest versions is called a Linear Congruential Generator (LCG). It uses this formula:

X(n+1) = (a × Xn + c) mod m

Where:

• (X_n) is the current value
• (a) is a multiplier
• (c)is an increment
• (m) is a modulus

You start with your seed, plug it in, and get a new number. Plug that in, get another number, and so on. The numbers may look random, but they follow quite a predictable pattern.

Why Not Just Use Random Numbers for Terrain?

Here’s the problem with purely random numbers: if you assigned every block a random height, you’d get something that looks like TV static. Spikes everywhere. Pits everywhere. Completely unplayable.

So Minecraft uses noise functions instead.

Noise functions produce values that smoothly change as you move across space. Nearby locations get similar values, so instead of chaos, you get gradual hills and valleys that actually look natural.

A simple version of this looks like:

Height = Noise(x, z)

Minecraft uses a 3D coordinate system:

• x → East-West direction
• y → Height (up and down)
• z → North-South direction

High values become mountains. Low values become plains or oceans. The transition between them is smooth, not jarring.

Perlin Noise: From slopes to mountains

source: https://viclw17.github.io/2018/12/28/Perlin-Noise-Implementation

The most famous noise algorithm used in games is Perlin Noise, created by Ken Perlin back in 1983.

The key idea is that neighboring points are related to each other. Look at this example:

See how the values go up gradually? When you convert those into terrain heights, you get rolling hills instead of messy, random spikes.

Minecraft layers multiple noise functions on top of each other at different scales. One layer defines the big mountain ranges. Another adds smaller bumps and details. Together, they create terrain that feels real.

2D vs 3D Noise

Minecraft uses two types of noise:

2D Noise : Works with (x, z) coordinates (think of it as a flat map). It’s used for:

• Terrain height
• Temperature maps
• Moisture maps
• Biome placement

3D Noise: Adds the vertical (y) coordinate too. This lets the game create things that exist inside the world, like:

• Caves
• Caverns
• Underground formations

2D noise builds the surface. 3D noise carves out the underground.

Biomes: More Than Just Aesthetics

Biomes aren’t placed randomly either. Minecraft generates environmental maps. The temperature, humidity, erosion, how “continental” a region is, all by using noise functions.

It then checks those values and decides which biome fits best:

• Hot + dry = Desert
• Hot + wet = Jungle
• Cold = Snowy biomes

Because the noise values change gradually, biome transitions look natural too. You don’t just teleport from jungle to tundra in two blocks.

Carving: How Caves Get Made

Once the solid terrain exists, Minecraft runs a process called carving. It samples 3D noise values underground and removes blocks wherever the value crosses a certain threshold.

Simplified version:

If Noise(x, y, z) > 0.8 → remove the block (make it air)

Do this across the entire underground, and you get a whole network of caves, tunnels, and caverns.

Modern Minecraft uses more advanced systems, but that’s the core idea.

Surface Details and Biome Finishing Touches

After terrain and caves are set, the game figures out what the surface should look like:

• Deserts get sand
• Plains get grass and dirt
• Snowy biomes get snow

This depends on biome, elevation, temperature, and nearby terrain. It’s what gives each biome its distinct look and feel.

Ores: Not Just Randomly Scattered

If ores were placed completely randomly, diamonds would be just as common near the surface as deep underground. That’d make mining way less interesting.

Instead, Minecraft uses probability distributions to control where ores spawn. Think of it like a bell curve for each ore type. here’s a height where it’s most likely to appear, and the further you go from that height, the rarer it gets.

Source: https://www.minecraftmaps.com/tools/ore-distribution

• Coal shows up across a wide range of heights
• Iron peaks at certain layers
• Diamonds concentrate deep underground

This is what makes mining actually feel like exploration. You have to go to the right depth to find what you’re looking for.

A Whole World from One Number

Here’s the full picture:

One seed initializes a fake random number generator, noise functions shape the terrain,biome maps figure out climate zones, carvers dig out caves, surface builders add finishing details, probability distributions decide where ores go.

And the scale of it is kind of mind-blowing. Minecraft can generate around 18 quintillion unique seeds. That’s 18,000,000,000,000,000,000 possible worlds! More than enough for every person on Earth to explore a completely different one, forever, and never run out.