Saturday, March 14, 2015

PLSS CadNSDI – PLSS and CadNSDI Basics

This is the third of a series of documents that describe the contents of the PLSS CadNSDI data set.

The Public Land Survey System (PLSS) was first and foremost an inventory of public domain lands designed to determine what the land assets and uses existed on the vast public holdings.  The measures and divisions on the land were used to parcel these holdings so they could be offered for sale or held for national use.  The public domain lands (sometimes called PD lands and the 30 states where these lands exist are sometimes called the PD states) are lands owned by the Federal government for the benefit of the citizens of the United States. Within the PD lands are non-PD lands such as land grants, tracts, and other lands that were occupied or owned prior to U.S. acquisition or prior to PLSS survey.  The original land inventory and surveys have become the basis for legal land descriptions.

There are many technical considerations and impacts to land rights that depend on when and how lands came into public or private ownership.  This document is not that description.  This document and all of the documents in this series describe the PLSS CadNSDI polygons (parcels) and the attributes and non-nominal configuration of these surveys and polygons.

The PLSS may appear to be a relatively simple system of hierarchical squares but in fact it is a very complex and highly variable system.  For every rule there are a myriad of exceptions.  For example, the simple fact that all PLSS Townships are defined as being north or south of a baseline is not even universally true as there are many PLSS Townships that are referenced East and West.

One of the most common misconceptions about the PLSS is that it covers all thirty states with a continuous and uniform grid of six-mile squares that are then further divided into one-mile squares. This couldn’t be further from reality.  The PLSS is NOT a mathematical system; it is a legal land division that is defined by corners on the ground that were established according to sets of instructions to surveyors that evolved over time.  The “rules of engagement” for land surveyors establishing the PLSS changed as the PLSS evolved.  What was true in one area may be different in another.

The PLSS is not all rectangular.  There are important components of the PLSS that are non-rectangular.  The rectangular PLSS is a simultaneous land description meaning that all of the lands covered by a rectangular survey were described in one survey and all of the lands within that described area of equal standing, meaning there are no junior or senior rights among equal levels of division.  The condition is commonly called a simultaneous conveyance or simultaneous creation in the parlance of land surveyors.

The elements of the rectangular PLSS are described in Chapter 3 of the 2009 BLM Manual of Instructions (The BLM 2009 Manual of Instructions is not available in digital form but information on ordering the Manual can be found at this link ( (last accessed March 2015)).  These are surveys where the PLSS contains elements that are defined with the nested hierarchy.  An irregularly shaped PLSS Township, fractional townships and half townships are all rectangular surveys.

Non-rectangular PLSS surveys are called special surveys.  They are described in Chapter 10 of the BLM Manual of Instructions, 2009 edition. Special surveys are created when it is necessary to protect an existing interest or pre-existing condition, such as when particular rights or interests have been designated by legislation and require a special surveying method or to separate federal interests from private or other non-federal interests.  In most cases the special surveys create “holes” in the rectangular data.  That is, in areas where a special survey is created, the underlying rectangular information is either no longer valid or never existed.  There are exceptions, as there are with all things cadastral.

General Rules for the Rectangular PLSS
·      The rectangular survey is a simultaneous conveyance
·      The polygons are created as a nested hierarchy
·      Surveys are not segregated
·      Lost corners within rectangular surveys can be re-established by proportionate methods because of equal rights among polygons

General Rules for Non-Rectangular PLSS or Special Surveys
·      They protect an existing private right
·      They carve out a new right
·      They may be measured by metes and bounds and may have crossing closing corners
·      They have a junior/senior right relationships for rights among themselves and with the rectangular PLSS
·      They may be segregated

Segregation is the process of defining lots (sometimes called government lots) around a non-rectangular PLSS survey to provide land descriptions for land that does not follow the regular quartering and halving for aliquot parts but are still lands in the rectangular PLSS land description system. 

If the lands have never been in the public domain (non-PD lands) the survey measurements and divisions are described in the Survey System feature class.

Polygon Identification Codes
Every polygon in the standardized data has a unique identifier or identification code.  These identifiers are “intelligent” in the sense that they are built from the polygon type and location.  The Subcommittee recognized that a sequentially assigned non-intelligent identifier is a preferred approach in database design references and texts, but given the volume of existing data, the preferences of users, and the challenge in building a nationwide systematically assigned non-intelligent identifier that would be recognized by the multitude of data producers would be difficult and costly to build and then effectively maintain.  Many states and local government have internal identifiers that can be used to construct the national standard identification code.

There are many online documents that provide extensive descriptions and discussions on the PLSS and its many nuances.  Some of these include

No comments:

Post a Comment