Naath - what do you mean by "map"? do you mean a neighbourhood layout like you see in this forum: http://www.insimenator.net/forumdisplay.php?f=495
if this is what you mean, these do not go in the Downloads folder like most other things.
The files associated with these go to the SC4Terrains folder
~(My) Documents\EA Games\The Sims 2\SC4Terrains