Minecraft wiki entry for Mapping, associated text: Tip: Surface lava pools make good landmarks as they show up as red dots on zoomed-out maps. The higher the zoom-level, however, the larger the pool must be before it shows up. You can, of course, make your own lava pool, just be sure it is open to the sky. To be safe, you can cover the lava pools with glass to keep players, mobs, and drops from falling in.