A parcel of property has 640 acres. 1 square mile, or 27,878,400 square feet, is a chunk of land. A square acre is 43,560 ft. A section is divided into 640 acres.
The ease with which the property can be divided into halves and quarters using whole-acre measures is one of the reasons for measuring land into sections of 640 acres. Without a strong background in mathematics, one may very simply divide a quarter section of land, or 160 acres, into quarters, or a quarter-quarter section, of 40 acres. A quarter-quarter section of land was the smallest land parcel that could be purchased in 1832.