The image is stretched to fill a rectangle of world coordinates. It defaults to your whole world border. Set the corner coordinates below, or use the buttons.
Type or paste one coordinate per line. I read most formats:
North base 1200 64 -800 — name then X Y Z-240, 70, 512 Spawn trap — coords then namex:100 y:64 z:-200 Mine · /tp 100 64 -200Hub 300 -900 @Steve @Alex #base — @ players, # tagsTwo numbers = X and Z (Y left blank). Unknown @players are created automatically. Everything is previewed below before saving.