The shape of a farm can depend on a number of factors, including:
Irrigation
Some farms require irrigation, which is often supplied from a central location. In these cases, the best way to grow the crop is in circles.
Geography
On steep slopes, farmers may have to construct flat terraces of land to farm. On less steep slopes, water running downhill can wash soil and nutrients off fields. Farmers may account for this erosion by planting crops along the contours of the landscape.
Land sales
In open areas, farms often look square because land is usually sold in (or divided into) squares.
Farms in relatively dry climates, such as Idaho, are often circular in shape due to the use of central pivot irrigation systems.
