I wouldn't use the map, though it's popped up a few times recently. What if someone passed parameters such as this?

C1 = 1
C2 = 1
C2 = 0
C2 = 1
C3 = 0
[download]

You'll end up with an array of (1, 1, 0, 1, 0) when you're only expecting three checkboxes.