Sector
A Sector is an 8x4 tile area (256x128 pixels) that defines various attributes of a map, such as its music, tileset, palette, and more.
When entering a sector via a warp (e.g., doors) or when refreshing the screen (e.g., by using the Sound Stone), any sectors that do not match the current sector’s tileset information will be hidden. These mismatched sectors will display as tile 0, with no NPCs visible.