Protraction Diagram

A protraction diagram is an official BLM drawing that extends the Public Land Survey System (PLSS) grid over land that has not been surveyed on the ground. It lets unsurveyed land be described by township, range, and section before any corners exist.

BLM's Manual of Surveying Instructions (2009) says protraction diagrams "have been prepared for substantially all unsurveyed areas in the public domain" and are prepared "to describe unsurveyed land areas" (section 3-12). It is equally clear about their limits:

• "A protraction diagram is not, and is not intended to be, a substitute for an official survey."
• The diagrams "consist of drawn lines that follow the public land survey system but are not an actual survey."
• They "do not involve a field survey with monumentation and hence no monuments on the ground."

BLM's Glossary of Surveying and Mapping Terms adds that a protraction diagram is approved for the Director by the Chief, Division of Cadastral Survey, and filed in the BLM state office "after public notice in the Federal Register."

What they are used for

Official protraction diagrams provide "a basis for the administration and management of unsurveyed Federal lands for all purposes short of conveying title" (section 3-138). They can become the basis of land location for leasing and for administrative boundaries such as wilderness, withdrawals, and selections. Alaska is the notable exception on title: the State of Alaska or an Alaska Native Corporation can elect to receive patent to certain lands on the basis of protraction diagrams (section 3-139).

BLM's Specifications for Descriptions of Land (2017) direct that unsurveyed land be described by "the subdivisions shown on the approved protraction diagram," with the acreage shown on the diagram.

Original and amended diagrams

Before 1993, corner positions on protraction diagrams were defined by bearing and distance from the exterior boundary of the protraction. Now they are defined by geographic coordinates, called Plan Of Survey Coordinates (POSC), and such diagrams are called amended protraction diagrams (section 3-141). Between the coordinate-based interior and existing surveyed lines, amended diagrams use protracted blocks of uncertain area, numbered from 37 or the next number above the highest already used, "to avoid confusion with section numbers" (section 3-142).

A caution from BLM

The Manual warns that the locations on protraction diagrams "are based on the best available evidence," and that "there are special survey parcels and leases described by legal subdivisions that are actually located miles from the location shown on the protraction diagram" (section 3-140).

Why it matters for mining claims

The Manual says placer mining claims on unsurveyed land "should be conformed as nearly as practicable to the protraction diagram" (section 10-140). A mining claim described by protracted section is only as accurate as the diagram. Where field conditions later require it, a protraction diagram can be abandoned and replaced by a new plan of survey (section 3-38), so research compares the mining claim's monuments, the protraction, and any later official survey.