Sections — First Divisions of Townships
The PLSS Townships are typically divided into 36 Sections (nominally one mile on a side), but in the national standard this feature is called the first division because Townships can be divided into non-section features. Most local governments, and even places where Townships are not sectionalized, the GIS attribute and feature will be called Sections or Section Number.
It is important to realize that not all townships are divided into sections and it is important to recognize the variations so you can identify these divisions correctly in land descriptions or in data use.
First divisions do NOT overlap and all first divisions in a Township should completely cover or completely account for all area in a PLSS Township, except meandered water areas. Typically, sections are numbered in Boustrophedon order from 1 to 36, nominally defining one mile square areas. Boustrophedon meaning the numbers move across the township back and forth from east to west and then west to east much as oxen would plow the ground. However, as with most things cadastral, there are many exceptions, so just be aware that sections are not always numbered starting with 1 in the Northeast corner of the Township, there can be more than 36 sections in a township, section numbers can be duplicated, and sections can be “missing”.
Normally the GIS should have a place for the section number, a label field, and if the jurisdiction has non-sectionalized townships than an attribute for the type of first division, either as a code or text, and an indication as to whether the area has been surveyed or protracted is helpful. If the jurisdiction has large non-PLSS rectangular areas such as Land grants or water Bodies, it is helpful to included the survey status (surveyed or protracted or extended) so that if the rectangular PLSS areas are extended across the large land area, it can be symbolized or labeled as an index or extended grid and not part of the legal PLSS.
Some of the more frequently occurring First Division types that are not sections are shown Lots, Protracted (or Protraction) Blocks, and Quarter Townships. Examples of each are shown.
Protraction Blocks or protracted Blocks are areas defined by the Bureau of Land management as a plan of survey. When a federal survey is executed in these areas the rectangular PLSS will follow the plan in the protraction diagram as closely as possible.
These townships were not sectionalized when the PLSS was first run. At a later date, the lands in these townships, which were originally Indian Reservation areas, were subdivided. The divisions were identified as lots not sections and they are not 1 mile by 1 mile.
It is not hard to find places in the PLSS with duplicated section numbers or irregularly defined section numbers. The main point is that the PLSS Township First Division, may or may not be a section and the dimensions will vary significantly from one mile by one mile. This further emphasizes the legal land description function of the PLSS. While it may look like a nice regular grid from an airplane, on the ground there a lot of exceptions. If you have an application that needs a regular guided cell, it is better to lay down a mathematical grid, than to rely on the PLSS divisions to be regularly spaced.