there not that hard to do , well not the basic paterns, the size of that one is large , but maybee there was a good few folk doing it.
to do circles , you put a stake in the ground tie cord to it and go round like a compas in maths.
to make the corn flat , you use a plank , hole drilled in each end with a length of cord wich is held in your hands and is tied in to each end of the board, you just then tred on the board and it flatterns the corn, release the presur with you foot, move farward and press down again, flattening more corn.