Even if land on Earth were infinite, there would still be differences in value based on location. Already there is desert land which can be used for free but urban land is far more valuable due to its proximity to desirable features.

Economic rent like this pops up even in human-made domains of potentially infinite expanse, such as the internet. There is no limit to the number of domain names which may exist yet some are far more valuable than those which can be claimed for low-to-no cost. Even social media platforms are valued to include the economic rent of their own user communities. For example, even if there came along a social media platform which was better than Facebook in every way, users would still value Facebook more because it has more community and community-generated activity and content.

There are grades of land. Land in the city is more scarce and more valuable. Rural land is less scarce and less valuble. Land on Mars is even less scarce and less accessible and less valuablee.

Same with domain names. People are interested in using shorter domains like abc.com, not long ones such as xyajfbeusnfdbdjak.craptld

The scarcity applies to a grade of land or string, not to all land in the Universe or string space in total.

It is difficult to compare the 'grades' of land, because the grading is not discrete but somewhat continuous.

I don't think that's the case in any remotely practical sense. If someone cannot get to the land and use it then they effectively don't own it.