Erzherzog Johann, the hills, themselves, are held together by rare earth magnets. This is shown in the third photo, beneath the header, "LARGE WALLED FARMS, plus MAGNETIZED HILLS & TREES. NAP WIP 6." The hills form a chain, held in place by the magnets.
They are beautiful, without doubt. I am not a fan of the fact that they form long rows. To be honest, they resemble a mound septic system drain field. His concept is amazing, solid: make sectional, modular hills, held together by rare earth magnets. His layout design is too regular, however.
I would suggest making quarter-hills, with magnets on two sides: form irregular hills by putting together four quarters, all different shapes, but with uniform heights and equal side lengths on the unfinished sides, such that they match up, when four are put together, with no seams showing. This would allow for greater variations, while still being compatible. Loads more work than what is shown, and what is shown is already a lot of work. Once completed, however, you would have a tremendously variable system of hills to work with!
He is leaning more towards the realistic, diorama appearance, end of the spectrum, which makes standing miniatures atop his hills, more challenging. I favor the other end of the spectrum: stepped hills, which will support miniatures fully, easily, without issue, but realism is sacrificed, of course (to be honest, I abandoned realism entirely, but you choose your position on the spectrum, and run with its limitations). Cheers!