Minecraft Forums

Quote from Akynth

The seed is the starting number used to initialize the pseudo-random number generator for the map creation algorithm. It does not relate directly to anything on the map.

Here's an incredibly simplistic example of how it might work:

Take your seed number. Square it. Keep two numbers from that: the first three digits, and the last digit. The latter determines the biome type: 0 water, 1-4 plains, 5-7 forest, 8-9 swamp. The 3-digit number is used for the next iteration.

So let's say we start with the number 123. That's our seed for the example. Square it, you get 15129. So the biome value is 9 (the last digit), and the next input to the generator is 151 (the first 3 digits). According to my very simple list above, this gives us a swamp biome. Cycle it again, 151 squared is 22,801. So this time we have a plains biome, and the next input is 228. Next time around we get 51,984, giving us another plains biome, and 519 to feed the generator. 519 squared is 259,081, so we have plains again, and 259 for the next cycle. If we do this for 8 cycles, we get:

swamp, plains, plains, plains, plains, water, plains, water

Now, if we started with the seed 234, it would work out like this:

forest, swamp, plains, forest, plains, plains, swamp, forest

123 always produces swamp, plains, plains, plains, plains, water, plains, and water (unless I can't type, of course!), and 234 always gives you forest, swamp, plains, forest, plains, plains, swamp, and forest, but nothing about those numbers indicates anything specific with regard to what biome goes where; it's just an initial seed for our incredibly simplistic pseudo-random number generator. The actual terrain generation in Minecraft is enormously more complicated than my deliberately very simple example, of course, and the RNG is more sophisticated than just "square the first three digits", but the principles are the same.