BlueMap

BlueMap is a program that reads your Minecraft world files and generates not only a map, but also 3D models of the whole surface. With the web app you then can look at those in your browser and basically view the world as if you were ingame! Or just look at it from far away to get an overview. BlueMap comes as a Spigot/Paper or Sponge Plugin, as a Fabric or Forge-Mod and you can also use BlueMap without any Server from the Command-Line as a standalone tool. If installed as a Plugin/Mod, BlueMap renders asynchronously to your MinecraftServer-Thread. This means at no time it will block your server thread directly. So as long as your CPU is not fully utilized, your server should not be slowed down while BlueMap is rendering.