tilemap collision help

i'm making up a tilemap level for my space game( when you reach a space station). i've got the tiles in and stuff but when it comes to collision, my engine works out collisions depending on whether or not your overlapping onto a nowalkable tile.

But a couple of tile are half floor and half wall

#=floor @=wall
where 2x2 characters = 1 tile

##
## =1 tile

@@@@@@@@
@@@@##@@
########
########

any ideas as how to go about this?

What I do is set up 4 "quadrants" for each tile.

Type Tile
  Field UL,UR
  Field LL,LR
End Type

That way, one tile can be broken up into 4 sections.

-cb

thanks for that! i've been kinda stumped on that :D