Measuring visibility

Is it possible at all to measure the amount of visibility a player has, and assign that value to a variable? I wouldn't think it would be, but I figured I'd ask anyway.

Basically I'm trying to make a map that gives you gold every 60 seconds in amount based on how much visibility you have. The idea is that, the more territory you control, the more money you get, but I don't want to use pre-defined regions like zone control or that Rome game.

I don't know of any commands in the editor that fit your exact needs, but you can use the condition:
(Boolean) Visibilty - Point is Visible to Player

You could set up a grid type thing around your map (using regions, trees, etc).