to check the tile

 ld hl,(mapstart)               ; address of the start of the map.  TOP LEFT TILE!!!
 ld a,(column)
 ld e,a
 ld d,0
 add hl,de                      ; shift it to the right, A pixels

 ld a,(columnLength)            ; width of map
 ld e,a
 ld d,0
 ld a,(row)
 ld b,a
rowMultLoop:
 add hl,de
 djnz rowMultLoop

; HL = current tile you are standing on.
ld a,(hl)                       ; get tile ID