The map now shows two zones: the charted one in a pale light, and the frontier in red.
Before this the frontier was simply black, and black on this map also means "nobody has walked here" - the two could not be told apart.
The line is drawn off the world border itself, so the picture and the wall a player walks into say the same thing.
The full list of changes
01Two zones
The charted half is a pale cold wash with a thin frame; the frontier is dark red with a bright line along the boundary.
Hover either one: the label says what is shown there, and what is never shown.
The zones can be switched off separately from the territories - they are a layer of their own.
02Why this is a fix and not decoration
Taking an area off the map leaves an absence, and an absence here already means something: ground nobody has walked.
So a world cut in half looked exactly like a world nobody had finished exploring. The map was not hiding anything - it was saying nothing.
Both halves are drawn now, and what lies between them is a line rather than a gap.
03A guard
If the world spawn ends up in the veiled half, the server says so in the log at start - because every new player would arrive where the map draws nothing.
It is a warning and not a refusal: where the line runs belongs to whoever holds the world.