the mapID can be found on the map on the bottom.
you would see 003, 34, 10 (this is MapID 3, X position 34 and Y position 10.
mapID, x, y is different for everyone depening on the map they use it for.
the same way, you make map transfers, you can select it by event commands
or by scriptcall, depending what you feel most comfortable with.
for example, you use mapID 5, and you dont want it visible, you use:
JavaScript:
$gamePlayer._opacity = 0;
$gamePlayer.reserveTransfer(5, -999, -999, direction, fade);
SceneManager.goto(Scene_Map);
this load mapID 5, x and y position on -999, even if it can move, it takes,
999 tiles, if that spot is blocked or around it, it can never reach it, even
if you use -1 or -5.
if you want it on the map rather than the top corner or 0,0 use the coordinates
that fits, next to the mapID on your map you want to go too.