The Land Ordinance of 1785 ordered the western territory surveyed before settlement into townships six miles square, each divided into thirty-six sections of 640 acres, numbered and sold at auction by the section, with one section reserved to support schools. Jefferson's committee had proposed the scheme in 1784; it became the Public Land Survey System that eventually covered roughly three-quarters of the continental United States. Land was thereby abstracted into identical numbered squares that could be described, priced, sold and mortgaged sight unseen from an office a thousand miles away, indifferent to river, ridge or existing indigenous occupation. The section line then became the road, the field boundary, the county line and finally the city block.
This is surveying as an instrument of state and market at continental scale - the moment land became a standard commodity traded on paper, and the moment the grid stopped being a city plan and became a national template. American urban form, from the mile-square arterial pattern of Chicago and Phoenix to the shape of the suburban subdivision, is that survey made visible.
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