My understanding is simply that they have used NASA height maps for creating the campaign map rather than a manually created one.

Thats something that most of the RTW mods have been doing for some time, though I get the impression that the Empire engine allows much higher quality height maps to be used than was practical on the Rome engine.

Also it looks like there will be a lot more in the way of terrain/climate types & some of that may come from satelite data too, presumably with manual alteration from research into changes since the game period.