How dit you set the tileMapData into a variable? I am also curious to find out what the width and height is. There is a function, TileMapData.isOutsideMap(x, y), but I am not sure how to use it. Instead of defining a tile as the random location the sprite starts at, I want to place the sprite at the bottom and middle of the tilemap. Maybe the width and height of a tilemap works differently than the location of a tile.
Maybe if you repost this issue under Arcade | Help, someone else might help.
https://forum.makecode.com/c/Share-your-Arcade-projects-here/help/14