The Measurement That Built America


The 640 acres that made up a section of a township could be divided into quarters, eighths, and sixteenths and still leave a whole number: 40, to be exact. This numerical neatness ensured that 40 acres became the basic unit on which Jefferson’s great landed democracy was built. Owning a 40 was the bottom rung on the property ladder, and to a surveyor nothing could be easier to measure. A 40-acre square was merely 20 chains by 20. Railroads sold land by the 40-acre lot. After the Civil War freed slaves were reckoned to be self-sufficient with “40 acres and a mule.” A nineteenth-century pioneer described how to pace it out on the prairie before the survey had even arrived: A walk 440 yards south, toward the midday sun, by 440 yards west, toward the setting sun, made a 40, and the claim could be registered later when the surveyor’s map was drawn up. The heroes of John Steinbeck’s The Grapes of Wrath were the dirt-poor farmers who scraped a living on dry, dusty forties in 1930s Oklahoma.


The survey was unified by running a number of carefully calculated north-south lines (known as principal meridians) and east-west lines (principal baselines) far enough to connect the work of one survey team with another. For example, the fifth principal meridian begins in Arkansas and runs all the way north to the Canadian border, connecting surveys in about 10 different states. Since the earth is not flat, the north end of a township is about 20 yards narrower than the 6 miles it is supposed to be. And the next township north is narrower still. The cure is to remeasure after four or five townships, bringing the distance back to 6 miles with a so-called correction line. In the Midwest, where roads tend to follow the survey lines, this produced a dead end and a sharp 90-degree turn after 24 or 36 miles of straight driving. You can tell by the skidmarks that it takes drivers by surprise.

The surveyor’s chain shaped urban America too. The average city block with surrounding streets covered 5 acres (5 chains by 10), and in Philadelphia, Salt Lake City, and innumerable other cities, the central square measured 10 acres (10 chains by 10). When Ferdinand R. Hassler was authorized by Congress in 1836 to produce the first federally approved set of weights and measures, he publicly declared his preference for the 10-based metric system, but he conceded that the choice “of a set of standards in general depends upon the individual use made of them.” For the United States, that could only mean the 4-based measures that the survey had spread throughout the nation. Every attempt to replace the U.S. Customary System of weights and measures with the metric system has failed, so far, because that Customary System is built into the very structure and values of American society.

This is the significance of what you see from the airplane window, an enterprise so massive, so integral to the United States, that it almost disappears into the landscape.