Section, PLSS Definition

A section is the fundamental working unit of the PLSS. Each township is divided into 36 sections arranged in a 6-by-6 grid. Sections are numbered in a specific serpentine pattern: beginning with Section 1 in the northeast corner of the township, numbering proceeds west to Section 6 in the northwest corner, then drops down one row and numbers east from Section 7 to Section 12, then drops again and numbers west, and so on. This boustrophedon (back-and-forth) pattern places Section 36 in the southeast corner and Section 31 adjacent to Section 6 in the southwest area.

The numbering pattern is fixed by federal law and is the same in every township across all 30 PLSS states. A surveyor or landman who knows the pattern can instantly identify which sections are adjacent to any given section. Section 1 is always adjacent to Section 2 (west), Section 12 (south), and the corresponding section in the township to the north (Section 36 of the township to the north shares a boundary with Section 1). This predictability makes PLSS descriptions highly efficient to work with.

A standard section measures one mile on each side and contains 640 acres. In practice, very few sections are exactly 640 acres. Survey errors, the curvature of the Earth, and physical features like rivers produce variations. The sections most likely to be non-standard are those in the north and west of a township — sections 1 through 7 on the north edge and sections 6, 7, 18, 19, 30, and 31 on the west edge — because these are where the township's accumulated survey corrections are absorbed. The excess or deficiency in acreage is distributed to the lots and aliquot parts in these border sections.

For GPS conversion, the section is a critical level of the hierarchy. A legal description without a section number is incomplete. Most PLSS coordinate calculators work by locating the section corners from BLM or state cadastral data and then interpolating the position of the described aliquot part within those fixed corner coordinates.