When building a model, the boundary between two objects can be drawn with perfect precision. When projecting this boundary into the real world, errors are inevitable. They may be related to measurement errors, ambiguity in interpretations, arbitrariness of criteria, the variability of natural objects, the complexity of law enforcement, and a multitude of other factors.
For example, the boundary between two plots of land was once drawn along a stream, and then the stream changed its course. One could continue to consider the boundary as following the stream, but this means a change in the area of one plot at the expense of the other. Alternatively, one could use the old cadastre, where each plot is a polygon with specific coordinates for its nodal points, and continue to consider the boundary as passing through unchanging coordinates, but this means it becomes less convenient to use, and effort must be made to mark it on the terrain.
Or, say, the boundary between plots was marked by a meter-thick wall made of wild stone. Now one of the owners wants to dismantle the boundary and put up an elegant thin fence five centimeters thick in its place. Who should get the area under the old boundary? Who should get the stones from the old boundary? Does a landowner have the right to touch the boundary at all without the neighbor’s permission?
The same applies to questions regarding to what height above the plot and what depth below the plot a landowner has the right to control access to their property. For instance, to grow crops, it is sufficient to control only the surface layer, but for mining minerals, it is necessary to understand whether a neighbor has the right to make claims because a well drilled from another territory has an inclined shaft and enters under their plot. To build a road, it is sufficient to manage the surface, where the application of property rights is most clear and obvious, but if it is necessary to fly a plane over this territory or lay a metro under it, this again raises questions about whether one needs to ask the landowner at all, and to what extent they are entitled to obstruct such endeavors.