To use this app, you have to submit a valid level.dat file of your savegame first. Either click the "Load.."-Button to open a file browser, or use an external file manager to drag and drop a level.dat file into your web browser.
Once the level.dat file is loaded, the spawn position will be shown at the top, and the spawn chunks will be highlighted on the map.
- green chunks are completely active
- yellow chunks do not trigger entity updates or chunk updates
- grey chunks are only partially active
See minecraftwiki for more information.
To scroll, use your arrow keys while your mouse cursor points at the map, or move your mouse while holding down down the left mouse button. You can use the slider below the map or your mouse wheel for zooming. The lower inputs allow you to go to a specific point (e.g., your base) of the map and set a marker there. You can always remove and add the marker by double clicking on the map. The "Save Map" button allows you to save the currently shown map as png image file.