You seem to assume the maps are being transmitted from the UAV.
They are almost certainly not (and if they are that's a poorly engineered system and I would be embarrassed that my government wasted my tax dollars on such a lousy design).
Maps are relatively static data, so it would be logical to store them on the computers at the ground control station (where you could have the entire world's terrain and likely aeronautical charts/airspace boundaries on your hard drive, along with current weather data and other useful information).
Moving the map to keep up with the position being relayed from the UAV is computationally trivial: iPads do it for real aircraft (ForeFlight & similar products) and your car's GPS system does it when you drive - neither system is as powerful as the typical desktop computer.
All the UAV would relay to the ground station is its position (and any other pertinent data dictated by its mission, such as photos/video). This arrangement minimizes the bandwidth required to control the vehicle, as well as its RF signature (less stuff to transmit back to base).
For autonomous UAVs, particularly ones which have to avoid airspace incursions, some subset of airspace data appropriate to the route of flight may be loaded on the vehicle, but I wouldn't call these "maps" - it's a much more compact representation of coordinates marking boundaries in 3D space (similar to the Jeppesen NavData products - possibly even using those products) . Such vehicles may also have terrain data loaded before flight if they lack other means to avoid collisions with terrain while operating autonomously.
Disclaimer: I have no experience with the RQ4 or any other military UAVs - this is just a common-sense engineering assessment.