copy pasted from another forum...
The TGA contains several identically-sized maps in one file. The maps, in order, are:
#1: Heightmap. A grayscale image that represents the topography of the map.
#2: Terrainmap. Each color on the terrainmap represents the terrain texture applied at the corresponding point on the landscape heightmap.
#3: Tint map. Used to tint the color of the corresponding point on the landscape heightmap.
#4: Blendmap. Controls how the terrain textures blend at the corresponding point on the landscape heightmap.
#5: Water map. Controls how the water plane intersects with the terrain (not 100% on this one)
#6: Water color map: Controls the tint of the water plane.
#7: Forest clutter map: each different color on this map corresponds to a different style of tree "clutter" that's applied at that point on the landscape heightmap.
#8: Small clutter map: same as #7, only for bushes, cacti, rocks, and so on.
