To make an 8km map, as Andy said you need very good knowledge and experience of 3DsMax, with also making BF2 staticobjects for it, as well as good knowladge and experience of the BF2Editors map editor and a good understanding of how heightmaps and other terrain systems work.
This is assuming we are talking about an 8km map that isn't 100% water or one with a tiny island in the middle.
It is possible to make an 8km, with a tiny island in the middle, using BF2's terrain but the terrain is seriously low quality, every grid square is 8m^2 (a 4km map like Kashan is 4m^2 and that's pretty low detail) and also the colour/detail textures are seriously low rez too (detail textures can be tiled up to keep them high rez, but there assigning area is much lower rez, although the low rez part is most notable on the colour maps). There are also some lightmap problems. The reason why it has to be on a tiny island in the centre as while you can scale up the heightmap via the code, so far no one has worked out a way of scaling up the terrain textures to cover the entire 8km area, instead its just limited to the 2km^2 or best, 4km^2 area in the centre of the map.
If your map is a 100% water map then its pretty easy to do, just need to edit the code
But if you want land all over the map, or most of the map like The Falklands, then you need to go into modelled terrain, which after doing the Falklands, I wouldn't advise anyone else to do it as its very complicated and got too many draw backs like no undergrowth etc.