The original surveys began in the late 1700’s and were performed with basic tools of the time: a compass and a 66 foot long chain.
The surveyors and the chain-men walked the survey line, aligning the chain with a compass bearing and stretching the chain as straight and level as possible.
Up and down hills and mountains, through swamps, streams and rivers, around trees and rocks, in wild territory and in all types of weather.
Many of the survey monuments were just piles of rocks and trees marked with a blaze cut by an axe.
Trees and rock piles from 200 and 300 hundred years ago that are now long gone.
And then there is the issue of spherical geometry - trying to lay straight lines on the curved surface of the earth.
An ancestor who fought in the Revolutionary War was given 1000 acres in Tennessee. He had to survey it himself. He and a friend spent many weeks in the bug infested brush surveying his grant. Only to find out the land had already been surveyed by another veteran of the war. My ancestor had to start all over.
>> then there is the issue of spherical geometry <<
And don’t forget about compass errors. I’ve seen colonial-era land surveys that were off as much as thirty degrees from True North — that is, much more than the “normal” magnetic deviation.
(Maybe the errors were sometimes due not only to pure carelessness, but also due to nearby iron-ore deposits?)