This made me wonder...are (most) of the (undisputed) borders of the world actually stored somewhere? Or are some stones and posts still the "official" borders?
In the UK (technically Great Britain in this context) at least, there is an open dataset available from the national mapping authority (Ordnance Survey), which is called boundary lines. It contains all of the different boundary lines and borders of local authorities, parliamentary constituencies, regions, nations etc. This is all geo referenced against the OSGB coordinate system. I could see interesting challenges in…
Likewise, the exact location of borders between properties is usually ill-defined. Only borders that have gone through a painstaking process of surveying and registering (usually after a dispute or on a new build) are exactly defined. Usually, when you move into a new house, you have a fence around your property, and the boundary is generally assumed to be inside the fence (with conventions for whose land the fence sits on that aren't always followed).
Adverse possession makes it more complicated. A neighbour decided to put up a new fence, and weren't nice about it. I stipulated (in line with the law) that no part of the new fence could be placed on my property (except parts under the ground surface). They decided to put the fence in the "wrong" way round, with the vertical posts on their property, and the fence attached on their side of the posts, effectively giving me sole access to the area of land in-between their fence posts. If I were to sell my house, the new owner would be quite reasonable in assuming that that land was theirs. After the requisite time, I could apply to have the land legally registered as mine, although the new laws mean that the neighbour would be informed and given a chance to "evict" me from the land - they would have to tear down their fence and rebuild it the right way round so that I don't have sole access to it any more. In this way, adverse possession effectively resets the boundary to where the actual fence is in practice every now and again, which means that the land registry doesn't need to store exact boundary locations.