Sitelines

The Grid

Posted on October 15, 2014 by Steve Bowie, AIA, NCARB, LEED Green Associate

The next time you look out an airplane window at the checkerboard pattern of farm fields, roads, suburbs and cities, and wonder why everything is in such a straight line, you can thank Thomas Jefferson.

President Jefferson believed that the fledgling American democracy would be encouraged if the nation was settled by many “yeoman farmers” living on relatively small pieces of land, rather than the massive estates owned by few, as was the case in feudal Europe. At the same time, the country was faced with debt from the Revolutionary War. The sale of new federal land west of the Appalachian Mountains to settlers would raise funds to pay off the country’s debt, but first it needed to be measured and divided.

The system devised is called the Public Lands Survey System (PLSS). It applies to most of the land west of the Appalachian Mountains. You might be unaware of the long-term influence this system had on the country and its culture, but references can be found everywhere. Townships, range lines, homesteading, city layout, “40 acres and a mule”, “the back 40” – all of these terms are related to the PLSS.

Land settled prior to the implementation of the PLSS was laid out in haphazard metes and bounds systems, with legal boundaries tied to local landmarks like prominent trees or rocks. Property boundaries in the east can be chaotic, and roads meander as they travel from one system to another. But beginning in eastern Ohio in 1785, land was subdivided in an orderly rectilinear and standardized system, opening up the west to development and settlement.

The process begins by establishing a base line for a particular region, running due east/west at a large scale of one or two states. A principal meridian was also set, running north/south. From these two lines, township lines parallel to the baseline and range lines oriented to true north, were set at distances of 6 miles apart. This two-dimensional grid forms an array of 36-square-mile townships, which in many areas have municipal authority to this day. This is why a parcel of land will sometimes be designated as being within a township, in addition to a city or village; townships often have a governmental and taxing authority.

Within each 36-square-mile township, the land is further divided into 36 separate 1-mile-square sections of 640 acres. These sections are in turn divided into 4 quarter sections of 160 acres, which can easily be further divided into four parcels of 40 acres each. This acreage was regarded as ideal for a single farming family to maintain, and was the amount of land offered to freed slaves after emancipation—hence the phrase “40 acres and a mule". Once the PLSS grid was established, networks of roads were built on township lines, range lines, and section lines to provide access to the farmland.

But discrepancies emerge when superimposing a two-dimensional grid system on the three dimensional sphere of the earth. At the scale of a mile, these discrepancies are barely noticeable, but scaled up to tens or hundreds or thousands of miles, they demand correction. Here's a common experience: Have you ever been driving on a country road that follows a straight line for mile upon mile, then for no apparent reason jogs to the left for a few hundred feet before resuming its course on a new line? This curious little jog represents the adjustment necessary in the range line between townships to account for the curvature of the earth.

Finally, one the biggest impacts of the PLSS is its influence on new cities that arose west of the Appalachian mountains, many laid out along these same lines, with arterial streets often exactly one mile or one half-mile apart, running in a north/south east/west grid. Midway Airport in Chicago completely occupies one entire section of land, exactly one mile square, with runways laid out on the precise diagonals of this section. Midway's runways are consequently shorter than most other commercial runways, as anyone who has ever landed there can attest.

So the next time you're driving through the countryside, or flying over America's vast farmlands, look closely and you'll see the great mind of Thomas Jefferson still evident in the country he helped create.