Customer explains the process:
The terrain info is part of any civil engineering scheme - when a new highway is designed, a company is hired to carry out a survey of the existing ground.
Aerial imagery is also part of the survey work - which is taken from LIDAR surveys (from helicopters), you can get both image and terrain data from a number of sites on internet but there are licensing problems with this approach.
Later, a digital model is created using specialist software like Microstation or MX. Then the model is split in 3DS Max into section if necessary.
Models can be cut from wood MDF or special plastic foam material.
The joint is designed in 3DS Max and once cut by the CNC router, is easily slotted in one another (like a Jigsaw)
See more examples here