The Nile floods, which changes the amount of ground that is arable. Since antiquity, it became important to measure land areas in order to assign them to farmers. Egyptians developed a catastral system, for which they needed to more ore less accurately measure surfaces of land. It included tools, but specifically trained people who could walk and record the number of steps from one place to the other ([ @dutka1993 “Eratosthenes' measurement of the earth reconsidered” ]).
Tools used that may be worth looking into: Khat (twisted cord of 100 cubits) to measure distances. Setats used to measure areas (is it a tool or a unit?). Merkhet to make straight lines over long distances. Gnomon (to measure the angle of the sun), and skaphe , an evolution of the gnomon.
It is important to keep in mind that many geometrical formulas came into existence while these measurements were taking places. It means that areas of non-rectangular shapes could have been easily miss calculated (also of triangles). There’s some archaeological evidence [ @dutka1993 “Eratosthenes' measurement of the earth reconsidered” ] regarding how they were over-estimating areas in ancient Egypt.
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