I don't bother with that confusing thing... I would reccommend making your own map editor and store the map as an array. Like this:
BGSCREEN 0,64,64
DIM MAP[64,64]
FOR Y=0 TO 63:FOR X=0 TO 63
MAP[X,Y]=Some number(Tile number)
NEXT X:NEXT Y
SAVE"DAT:SOMETHING",MAP 'Saves map data
LOAD"DAT:SOMETHING",MAP 'Loads map data
FOR Y=0 TO 63:FOR X=0 TO 63
BGPUT 0,0,MAP[X,Y]
NEXT X:NEXT Y
