Chain!
The theory behind surveying practice has never been the notion of the surveyor. It is rooted in a far older idea shaped by the sovereign that all land was held under. Physically and literally defending the land is where rights to land emanated from.
We have gradually tried to tame physical force with law to give a veneer of civility to our society, however the absoluteness of physical possession remain as a basis for the ultimate claim to land. This principle is reflected in modern real pr