Original suggestion
Right now, when two players are on different surfaces in multiplayer, the map shows the other player's position by simply taking his coordinates on his surface and displaying him at those coordinates on the other surface.
To improve this, I suggest that, if Player 1 is on Surface A and Player 2 is on Surface B, Player 1 is shown Player 2's map icon at the location where Player 2 last left Surface A, or not at all if Player 2 was never on Surface A before. In that case the player icon could have a different shape.
With Factorissimo, for example, this would accurately show people where they can find other people, by guiding them through the proper factory entrances.
To provide the old behavior with surfaces that are actually designed to be parallel (like z-levels), surfaces could have an optional surface_group construction argument that defaults to something unique, like the surface name. Surfaces in the same surface group would share their "last seen" locations, players would be displayed as before if they are on different surfaces in the same group, and player icons could have yet another different shape for that situation.
To improve this, I suggest that, if Player 1 is on Surface A and Player 2 is on Surface B, Player 1 is shown Player 2's map icon at the location where Player 2 last left Surface A, or not at all if Player 2 was never on Surface A before. In that case the player icon could have a different shape.
With Factorissimo, for example, this would accurately show people where they can find other people, by guiding them through the proper factory entrances.
To provide the old behavior with surfaces that are actually designed to be parallel (like z-levels), surfaces could have an optional surface_group construction argument that defaults to something unique, like the surface name. Surfaces in the same surface group would share their "last seen" locations, players would be displayed as before if they are on different surfaces in the same group, and player icons could have yet another different shape for that situation.
