In standard rules Alpha Strike, woods is a binary yes/no. If there are Woods intervening or occupied, there is a +1 Woods modifier.
If you want per 2" (or per hex for hex play) Woods, the Advanced Terrain rule adds that along with different levels of Woods (light, heavy, etc).
In standard/non-hexed AS, partial cover is determined by how much of the target is covered when looking at it from the attacker. Distance from the cover doesn't matter. In hexed play, partial cover is on p70 and mentions having to be adjacent to the partial cover and the partial cover being between the attacker and target.