Fractional Section, PLSS Definition

In the ideal PLSS grid, every section is a perfect one-mile square containing exactly 640 acres. In practice, this is rarely achieved. Fractional sections arise wherever the rectangular survey grid meets a physical or legal boundary that cannot be adjusted to fit the standard dimensions.

The most common cause of fractional sections is the presence of navigable water bodies. When a river, lake, or other navigable water runs through a township, the sections it crosses are bounded by the ordinary high-water mark rather than extending to their nominal dimensions. The remaining land in those sections is less than a full section and is designated fractional.

Fractional sections also occur at the western and northern edges of townships. Because the PLSS accommodates the curvature of the Earth by using correction lines, the townships bordering the west range line and the north township line are often slightly narrower or shorter than the standard six miles. The sections in these border positions — typically sections 1 through 6 along the north and sections 7, 18, 19, 30, and 31 along the west — are frequently fractional.

State and international boundaries create additional fractional sections. Where a state boundary cuts through a township, sections on that edge may contain only a portion of the standard acreage. In all these cases, the irregular parcels within fractional sections are assigned as government lots with specific lot numbers rather than standard aliquot part descriptions. The actual acreage of each government lot is recorded on the original BLM survey plat.