About The Metroid Map
In the Metroid game's program the world map is stored in a 32 by 32 grid of screen indices. The map does not specify which level each screen belongs to, only the screen index. This is important to understand. As you play the game and scroll from screen to screen the game simply loads the screens from the level you are currently in. When you go up or down an elevator the game loads data for a different level, and from that point on the game will display screens from the level you have newly entered. In other words, the game infers which level each screen on the map belongs to.

Editroid's map, or the "editor map," uses color coding to indicate which level each screen belongs to. But this information is not taken from the ROM, since this information is not contained in the ROM in the first place. Editroid can not infer which level each screen belongs to. The first time you load a ROM, Editroid guesses which level each screen belongs to. If it guesses wrong, you need to make the necessary corrections to the editor map. Every time you save the ROM, the editor map is saved along-side the ROM data.

Simply changing the colors on the editor map will not necessarily have any change in the game, and it is very possible to make the map in the editor to show something different from what will be seen in the game. When a room is added to the map, the level it will belong to should be marked on the editor so that the editor will know which level's data to use when the screen is displayed and edited. It is also important to remove a screen from the editor map if it will no longer be used, in order to maintain organization.

Screens that appear black in color on the map are marked in the game data as inactive. During game play, the screen will not scroll into these rooms. If an unobstructed path leads to an inactive screen then the player can walk off the edge of the screen and will not be able to see Samus (and, most likely, won't be able to get back into the visible part of the level).

How To Use The Map Editor
Left-click a screen to bring it up for editing. If you want to delete a screen from the map, right-click it. To "paint" on the map, hold shift and then left-click on a square that is the color you want to paint with, and then, without lifting the button, drag the mouse to copy that color to adjacent map locations. To cycle an individual map location through different levels, hold shift and right-click that map location. You can also use the number pad to change the selected screen on the map.