Bava Batra 106 - Selling a Field by Landmarks
If a seller stated that he was selling a field of a certain size, and he also identified the field by its landmarks and boundaries, he has made two contradictory statements. "Within these landmarks and boundaries" means selling as is, no matter what the size. The fact that he added the size of the field compels him to at least come close to this size.
If the field was found to be of a different size, then if the difference is less than a sixths, the field becomes the buyer's without any adjustment. If the difference is greater than a sixth, they have to make an adjustment, with the seller or the buyer paying the difference.
This 1/6 is not the same as overcharge , since there is no overcharge law for land . Rather, it is an estimate of what people forgive.
Art: Camille Pissarro - Enclosed Field at Eragny