The land north of the Ohio River and west of the Appalachians was to be surveyed and marked off in a rectangular pattern--with east-west baselines and north-south ranges--before any of it was sold. This territory was to be divided into townships six miles square, with each township in turn cut up into thirty-six numbered sections of 640 acres each. Land was to be sold at auction, but the minimum price was set at one dollar per acre, and no one could buy less than a section of 640 acres, which meant that a very substantial sum was needed for any purchase. In each township Congress retained four sections for future sale and set aside one other for the support of public education. Although only seven ranges were actually surveyed in southeastern Ohio, this policy of surveying in rectangular units became the basis of America's land system.