An initial seed is computed and stored in the game save file Based on this seed, the world is pseudo randomly computed, using a certain chunk/block/tile size (e.g., 32x32, 128x128) The world map is only generated on-demand, that is, as far as the player can see When a new chunk is discovered, its blocks are computed and persisted in the save file If there are no active components in a chunk that is not visible, the game will obviously not render it, it will only simulate it (position, item, velocity, etc)