You may have wiped your server and realize the minimap stayed the same. This is because the minimap data is stored client side on each player's computer.
This means, each player will have to use this guide to remove the minimap data to reset it.
1. Press ⊞ Win + R
on your keyboard.
2. In the run box, paste %USERPROFILE%\Zomboid\Saves\Multiplayer
3. Here, you'll see folders with the IP and port of all of the servers you have connected to.
4. Remove the folder that is named after your server's IP address and port.
5. Start Project Zomboid and the minimap data will return to normal.