Why chunks matter
The server loads, saves and sends the world one chunk at a time. Farms that should run together need to be in the same loaded chunks, and some, like slime farms, depend on which chunk they're in.
Press F3 + G in game to draw chunk borders. F3 also shows the chunk under "Chunk:" as your position inside it and the chunk's coordinates.
Region files
Each region file covers 32 × 32 chunks, or 512 × 512 blocks, and is named r.X.Z.mca. Overworld regions live in world/region, the Nether's in world/DIM-1/region and the End's in world/DIM1/region (Paper keeps them in world_nether and world_the_end).
Deleting a region file makes the game generate that area fresh next time someone goes there. It's a quick way to reset part of a map, or to get new terrain after an update. Stop the server first and keep a backup.
The maths
| Value | Formula |
|---|---|
| Chunk X | floor(block X ÷ 16) |
| Position in chunk | block X − chunk X × 16, from 0 to 15 |
| Region X | floor(chunk X ÷ 32) |
Z works the same way. Negative coordinates round down, so block −1 is in chunk −1, not chunk 0.