Correction Line

A correction line is the older name for a standard parallel in the Public Land Survey System (PLSS): an east-west line where the survey is corrected for the narrowing of townships toward the north. BLM's Glossary of Surveying and Mapping Terms directs readers from "correction line" to "standard parallel," and its standard parallel entry begins: "Also called 'correction line.'"

BLM's Manual of Surveying Instructions (2009) confirms: "The term 'correction line' was used for what is now called the standard parallel" (section 7-19).

What it corrects

Range lines run on true meridians, and meridians converge. The Manual explains that the range lines "would converge and intersect at the North Pole," and "the convergency is taken up at intervals by the running of standard parallels, on which the measurements are again made full" (section 1-30). The glossary adds that standard parallels "are established to correct for the convergence of range lines and to maintain a workable adherence to the requirement that each township be 6 miles square."

Spacing

Standard parallels are run east and west from the principal meridian "at intervals of 24 miles north and south of the base line" (section 3-13). The Manual notes that "there were many exceptions in the older surveys" (section 1-30). Where parallels were earlier placed 30 or 36 miles apart, an intermediate standard parallel may be run and given a local name, such as "Fifth Auxiliary Standard Parallel North" (section 3-13).

Standard corners and closing corners

A correction line carries two sets of corners. The Manual describes "offsets in the range lines and two sets of corners, standard corners for the lines to the north and closing corners for lines to the south" (section 1-30). "The corners first set in the running of a correction line are called standard corners. Those that were set afterwards at the intersection of a meridional line are called closing corners" (section 7-19). Standard corners are marked "SC" (sections 4-26 and 4-31).

Lost standard corners are restored by their own rule: "by single proportionate measurement on the line connecting the nearest identified regular standard corners on opposite sides of the lost corner or corners" (section 7-18).

Not the same as a sectional correction line

A sectional correction line is a different line. The glossary defines it as "a latitudinal section line run to rectify a defective latitudinal governing boundary," run on a cardinal bearing to a closing corner on the opposite boundary. It fixes a defective township boundary inside a township, not the convergence of meridians (see also Manual section 3-17).

Why it matters in research

Townships north and south of a correction line do not line up. A corner set for the sections to the north is not the corner for the sections to the south, and sections along the line often contain irregular lots. A mining claim tied to "the section corner" on a standard parallel has to be checked against the field notes to see which corner, standard or closing, was actually used.