I tried to do something like that in my New York challenge map, if you want to take a look.

The ideas I came up with to make things look like digital readouts were
--to overlay a square grid shrunk down reeeeeally small in order to give the impression of pixels wherever there were fields of color
--apply a soft 'outer glow' effect to just about everything on the 'screen'
--Wireframes (with variable width to imply depth) with an 'outer glow.' I would probably do something similar with the environment's contour lines--easy to do since those look like real-world maps, so getting contour line maps would probably be a piece of cake.
--emulate the UIs that we might have seen in super cheesy, late eighties to mid-nineties sci-fi/hacker films (anything from Tron to Johnny Mnemonic.)