Type these in the in-game chat (press Enter to open chat).
!pindrop an unnamed dot where you stand!pin <text>drop a dot with a label!pin <type> <text>a typed pin, e.g. !pin house Base!undoPinremove your most recent pin!deletePin <text>remove the pin matching that text!deletePinwith no text, removes your most recent unnamed pinEach row of the sidebar's Legend is a switch, remembered by this browser; the Layers card on the map holds presets of them, details (torches and fires, deaths, trails), and swaps the ground between the terrain render and a flat atlas of biomes (L cycles). Zoomed right in, builds turn from roofs into a floor plan; hide floor plan when close to keep the roofs. Portal lines join linked pairs, and a grave is gear still lying there.
Press M in game and turn on visible to other players. Without it you still show in the online list, but never with a location.
Players and pins refresh every few seconds; builds and the explored mask every minute while someone has the map open.