The Public Land Survey System (PLSS)

Lets get this straight right off the top: The Public Land Survey System (PLSS) is NOT a spatial coordinate system. The PLSS is technically termed a land partitioning system; i.e., a system that is designed to divide land into parcels. However, a lot of people attempt to use the PLSS as if it were a spatial coordinate system, often with less than satisfactory results.

The PLSS was created in 1785 by the U.S. Federal Government (via an act of Congress called the Land Ordnance Act). The PLSS had only one purpose: To facilitate disposal (either via sale or simple giveaways) of lands west of the Appalachian Mountains that the U.S. government had acquired from the British after the end of the Revolutionary War. Disposing of this land was a very high priority for the young U.S. Government, for a wide variety of reasons: U.S. soldiers had been promised land in return for their service during the Revolutionary War, the government needed the money from the land sales (there was no tax system in place at that time), and settlers were needed in the western lands to defend the nation's frontier from ongoing indian attacks.

What the nation needed was a very easy to use system of dividing land into parcels that could be sold or given away. The system had to be flexible; it had to be able to divide land into parcels of many different sizes. The system also had to be easy to use, because to a large extent, it was going to be implemented by frontiersmen with little or no formal education or training. Finally, the system had to be as unambiguous as possible; it would never do to have a system whose parcel boundaries were open to debate -- this would lead to disputes over land ownership (how many western movies have you seen where the antagonists are fighting over some disputed piece of land -- this is what the PLSS was trying to avoid).

The PLSS was the U.S. government's attempt to meet all of these goals. The PLSS has been the target of criticism and scorn for over 200 years, but the fact remains that it was largely successful in accomplishing its goals. The PLSS did divide land into parcels of just about any size, it was successfully implemented by frontiersmen with little or no formal education or training, and it did produce relatively unambiguous parcel boundaries. It was certainly far from perfect, but it worked. Much of the criticism of the PLSS could more appropriately be leveled against the government organization that administered it -- the notoriously corrupt (and now defunct) U.S. General Land Office. The PLSS itself was largely successful; but the organization that administered it was, unfortunately, a source of many problems.

In general terms, the PLSS is relatively simple; but as the old saying goes, the devil is in the details. The PLSS is basically a Cartesian system. PLSS surveys begin by arbitrarily selecting an origin for the Cartesian coordinate system. This origin is called the initial point. Often, prominent landmarks (e.g., rock formations, confluence points along rivers and streams, or even large trees) were chosen as initial points, but in many parts of the U.S. (such as much of the great plains), prominent landmarks are scarce. Thus, many initial point are simply undistinguished locations in the middle of nowhere. Overall, there are dozens of seperate initial points in the PLSS; Figure 1 shows some of these.

This Figure Under Construction! Expected completion date: 1/21/02

Figure 1. Some of the Initial Points, Base Lines (Geographer's Lines), and Principle Meridians of the Public Land Survey System (PLSS)

Once an initial point was established, professional surveyors measured the line of latitude passing through the initial point. This line of latitude was termed a base line (base lines were sometimes called geographer's lines; surveyors were called geographers back in those days). The surveyors also measured the line of longitude passing through the initial point; this was termed the principle meridian (Figure 2). Note that it is customary in the PLSS to identify each initial point by the name of the principle meridian passing through the point; neither the initial point itself nor the point's base line have unique names.

Figure 2. The arrangement of an initial point, the associated principle meridian and base line, and the subsequent township and range lines in an ideal PLSS survey.

Once the base line and principle meridian had been established, the surveyors went to work measuring township lines along lines of latitude at six-mile intervals north and south of the base line (Figure 2). They also measured range lines at six-mile intervals east and west of the principle meridian (Figure 2). Collectively, this process divided the land into square parcels six miles on a side (36 square miles in area), bounded on the north and south by township lines and on the east and west by range lines. Each 36 square mile parcel was called a township. The townships were identified by their position east or west of the principle meridian and north or south of the base line (Figure 3).

Figure 3. Naming the townships in the PLSS.

Here's where problems start to develop. The PLSS as we've described it up to now is a simple Cartesian system, with the initial point as the system's origin, the base line as the X axis, and the principle meridian as the Y axis. Distances along the axis are measured in units of "townships", with each township being six miles in length. Unfortunately, as we've seen in previous learning guides, you can't put a Cartesian coordinate system onto the curved surface of the Earth without some distortion, and the PLSS is no exception to this rule. The Cartesian PLSS system we've described so far can't continue for very long without encountering these distortions.

The biggest problem facing the PLSS is caused by the fact that the system's range lines run north-to-south, and thus they follow lines of longitude. Lines of longitude are not parallel; they converge as you move from the equator to the poles. Thus, instead of being a nice, simple Cartesian grid of symmetric squares six miles on a side as shown at the beginning of the animation in Figure 4, the townships defined by the PLSS are actually odd-shaped polygons that get smaller as you move closer to the poles, as shown at the end of the animation in Figure 4.

Figure 4. The north-south lines in the Public Land Survey System (the range lines) must converge as they approach the North Pole. This causes the areas of the regions between the lines to decrease as you move from south to north, and makes the PLSS a very imperfect Cartesian coordinate system.

Clearly, something had to be done to decrease the distortions in the PLSS down to an acceptable level. What was done was to insert standard parallels at every fourth township line and guide meridians at every fourth range line (collectively, standard parallels and guide meridians are often called correction lines). Basically, along these correction lines, the six-mile separation of township and range lines was reestablished. This made for a distorted pattern of "super townships," 24 miles on a side, that is very characteristic of the PLSS (Figure 5).

Figure 5. The impact of standard parallels (in blue) and guide meridians (in green) on the PLSS.

The final result of all of this was a collection of townships, each of which was at least close to being a square 6 miles on a side, that spanned much of the United States. States that were already part of the U.S. prior to the passage of the Land Ordnance Act in 1785, or states that were already surveyed when they entered the Union (like Texas and Hawaii) were not resurveyed using the PLSS. Similarly, federal lands that were not to be disposed of (like military reservations, national parks and so on) and indian reservations were not surveyed. The townships in the PLSS are shown in Figure 6. Click on the image in Figure 6 to see details of the PLSS in a few states. It is obvious that some of the townships aren't even close to being square (many have only three sides), and many aren't 6 miles on a side. However, the majority of the townships do come at least somewhat close to the ideal.

Figure 6. Townships in the Public Land Survey System (PLSS) in the United States (Lambert Projection). This image is clickable; click on any state to see a more detailed view of PLSS townships in that state.

Once the country is divided into townships, its relatively easy to divide the townships into smaller parcels. Each township was divided into 36 one-mile square units called sections. The sections were numbered using the odd, sinuous pattern shown in the middle portion (the red portion) of Figure 7. Each section could be divided into quarters; the quarters were (logically enough) identified as either northwest, northeast, southwest or southeast (Figure 7). Since a section covers one square mile, and a square mile contains 640 acres, a quarter section covered 640 ÷ 4 = 160 acres.

Figure 7. Dividing townships into sections, and dividing sections into smaller units, in the PLSS. In this example, if the principle meridian shown in the top of the Figure is named the "Fred Principle Meridian," the full description of the highlighted 10 acre subsection would be "Northwest quarter of the southwest quarter of the northwest quarter of section 34, township 2 south, range 1 west of the Fred Principle Meridian."

To identify parcels smaller than 160 acres, the PLSS simply continues to divide larger parcels into quarters. Thus, a 160 acre quarter section is divided into four, 40 acre quarter-quarter sections (once again identified as northwest, northeast, southwest or southeast), which in turn can be broken down into four quarter-quarter-quarter sections of 10 acres each, and so on (Figure 7).

As a land partitioning system, the PLSS isn't perfect, but its weaknesses and deficiencies are manageable. Unfortunately, as a spatial coordinate system, its hopeless. With its non-square townships, its skewed grid of township and range lines that is periodically interrupted by correction lines, and its assortment of initial points sprinkled randomly throughout the U.S., at best the township and range coordinates of a point make up a horrendously crude and inexact Cartesian coordinate system. Over the years, this fact hasn't stopped people from trying to use PLSS coordinates as if they were Cartesian coordinates, usually with disastrous results. Inevitably, these folks berate the PLSS as being a poor system. However, it really isn't fair to criticize the PLSS for this failing, because the system really was never designed to function in this way. The PLSS is a workable land partitioning system; it was never meant to be used as spatial coordinate system. Those individuals who insist on using the PLSS for a purpose for which it was not designed bear the responsibility for failure; the fault does not lie with the PLSS.