Rigid land ownership seems to be the source of a great deal of our troubles.
Been there, done that, it is worse than the alternative. People will stop cultivating anything, because why bother if a random officer can just take things from you at will.
Western regulations about land appropriation are strict for a reason, and they always require just compensation for a reason. That is the only way to prevent powerful people from just grabbing what they want, cloaking the thieving act in word bubbles about common prosperity.
Maybe there could be some balance instead of "Either everything can be owned, or nothing is!".
It isn't impossible to move cities if it's really needed and someone is footing the bill, even in a democratic Western country that is famously highly regulated, like Sweden. Since a mine in the north is expanding, they have to move the entire city (paid by the mine's operator in this case), building by building, which of course isn't without complaints, but it's a thing that actively being done as we speak. https://www.bbc.com/news/articles/cde3xp4xlw9o
But such situations are relatively rare. Perhaps the mine in Kiruna is worth it and the corporation/government can pay for the compensations. Same for vital ground communications (highways, railways).
If it isn't, though, then let the ore in the ground and let the people live where they built their homes.
Most of the time I hear ideas about "flexible ownership" etc., upon further discussion, the person starts talking about outright expropriation from people they don't like.
For a more likely scenario, see Japan. Demographic crash (which is already happening all over the developed world) followed by mass migration to urban centers with economic forces dooming or favoring a city depending on it's circumstances (looking at you, Miami).
But places like the Roman Empire absolutely had "hard" demarcations in some places, not just standard country borders, but also internal borders.
For example, when Caesar crossed the Rubicon, he legally crossed into Italy by doing so and thus triggered a war. Rome itself had pomerium, a city demarcation whose crossing had legal consequences as well.
If you entered the Roman Empire peacefully, and you had something to tax or apply duties to, you would be confronted with officials in the closest suitable place.
That sounds like border to me.
Borders are very much not a new concept. Nations are new-ish but not the idea of owned and protected land.
https://en.wikipedia.org/wiki/Sasanian_defense_lines -- https://en.wikipedia.org/wiki/Limes_(Roman_Empire)
Native American nations and tribes didn't "own" land in the way that European colonizers did, under a doctrine of private property, written deeds and legal systems. Even under tribal territories, access was fluid.
America and its land was held communally by tribes and was generally understood in terms of use rights. If your nation, family or tribe cultivated a field, you had rights to that field as long as you actively used it. And stewardship of the land was seen as something to care for, not a commodity.
And this was the way things were in America up until a few hundred years ago.