Visions

Skill Level	Displays	Range
Basic	Size of wandering stacks and willingness to join	greater of 3 and (Spell Power)
Advanced	Troop composition and Primary Skills of enemy heroes	greater of 3 and (Spell Power * 2)
Expert	Enemy town statistics and garrison composition	(Spell Power * 3)

Be advised, this spell does NOT nullify an enemy Hero's Disguise spell. He will still see the numbers, but not the correct creature types.