According to this Wikipedia article, Eurasia covers a land area of around 55,000,000 square kilometres (21,000,000 sq mi).
Even if your height markers were 10 metres apart, that would still use up a lot of drive space, so that’s one restriction.
Another is time. I would be surprised if one person could walk all over that large an area in a single lifetime, even if it were flat and free of obstructions. Daggerfall has an area of about 161,600 square kilometres, and according to the developers it takes about two weeks (real time) to walk from one side of the map to the other.