I used this tool at my degree a couple of lusters ago to do cartography with aerial orthophotos. We used it on cartography and geomorphology subjets.
The method consists on using two consecutive but overlaped orthophotos (on east-west direction) taken from a plane, so an optical effect allows you to see the relief. Then you can delimite units with a marcker pen on a transparent film. We after transpose the cartography to a topographic map.
My question is if this tool is still used at university and among working geologists.