diff --git a/Design-Doc%3A-%60level%60-tool.md b/Design-Doc%3A-%60level%60-tool.md
index bf7ade9..a471c58 100644
--- a/Design-Doc%3A-%60level%60-tool.md
+++ b/Design-Doc%3A-%60level%60-tool.md
@@ -76,5 +76,5 @@ For (number of component instances):
 For plane A and plane B:
    For (total tiles height):
       For (total tiles width):
-         2 bytes: Tilemap ID
+         2 bytes: Tilemap ID (0 = No Tile, otherwise offset by 1 in the tilemap)
 ```
\ No newline at end of file