Thats the C79 OPtical Sight. Its on pretty much every single rifle and their even on most C9 LMG's.
I personally hate them. Can't see anything through them at night. They have a glowing part, but its tough to acquire the target at night with the sight. I think iron sights would be better. For perfect clear day shooting, the sight works great. But usually it's not a perfect day.
It's 3.4X magnification.
http://www.sfu.ca/casr/101-c7a1.htm
And your tyalking about "looking over a whole lotta land".
Max effective range of one C7 is 400m. A whole section's mex effective range is around 800m I think. If you think you're going to hit anything over 400m by yourself with an M16/C7, you got another thing coming. That guy is probably looking at 2 kms to the road, although its tough to tell.