Tuesday, April 7, 2015

PLSS CadNSDI – PLSS Second Division (Aliquot Parts and Government Lots)

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

The PLSS Second Division is most commonly aliquot parts (areas resulting from equal halving and quartering) and government lots (or lots).  The PLSS Second Division contains all divisions below the First division, meaning that in some areas this may be quarter sections and in other areas it may be sixteenth areas.  Some implementations add another feature class for the Quarter Section only and put all divisions below the quarter section in the PLSS Second division.    These variations are compliant with the intended standard implementation.

Second divisions at the same level of division do NOT overlap.   Second divisions may or may not cover the entire first division because every section is not fully subdivided. The attributes for the second division are shown below.

Concatenation of the principal meridian, township, range, and duplication code that form a unique identifier for the township.
Township Identifier
Unique identifier for the first division.
First Division Identifier
Unique identifier for the second division.
Second Division Identifier
Code of the type of second division.
Second Division Type Code
Second division type text description
Second Division Type Text
Second division number or aliquot part reference.
Second Division Number
Second division suffix. Second division suffix used to identify duplicates or suffix to the name
Second Division Suffix
Notes about the second division of the PLSS such as R for replaced or other notes about the use and interpretation of the second division information
Second Division Note
PLSS Second Division label for cartographic output or web display.
Second Division Label
Code for the type of special survey typically from the codes for the BLM data collection.  Used in this feature to indicate if the feature is unsurveyed or unprotracted.
Survey Type Code
The description of the survey type code.  This is a description of the survey type, or survey status in the case of this feature, without a code.
Survey Type Text
The date of the source document
Source Doc Date
The reference to the source document could be a reference to a map or plat or a deed. This could include document type.
Source Doc Link or Reference
The record or recorded area as a text field. This may include the units of area as well.
Record Area Text
The record or recorded area as a numeric field
Record Area Number
The area of the feature in acres - computed from the GIS, this is not the record area.
GIS Area Acre

The second division types are listed below

Second Division Type Code
Second Division Type Description
Aliquot Part
An aliquot part is a division made by halving and quartering a section.  These are identified by the cardinal position such as Northeast (NE). 
Remainder Aliquot Part
Remainder Aliquot Parts are residuals or portions or significantly smaller than nominal aliquot parts.  These may be left over after a special survey or other survey cuts into an existing aliquot part and a portion of the aliquot has not been designated as a government lot and is remaining as an aliquot part. 
A subdivision of a section that is not designated as an aliquot part of a section and is identified by a number. A Government Lot, or Lot, may be regular or irregular in shape.
Quarter Section
A quarter section is an aliquot part that divides the section into quarter parts only.  In most cases quarter sections will be coded as A and the distinction between aliquot part and a quarter aliquot part is a state-by-state preference.  The preferred coding is to use A for all aliquot parts.
Unnumbered Lot
An unnumbered government lot is an area of land that appears to be a government lot because of its location in the section and its acreage.  Because Government Lots must be surveyed and have a number, it is expected that existing unnumbered government lots will gradually transition to either remainder aliquot parts or remainder government lots with a number.
Remainder Lot
A Remainder Government Lot or Remainder Lot is a residual or remainder or portions of  a Lot.  These may be left over after a special survey or other survey cuts into an existing Lot.
U *
Unsurveyed Protracted
Unsurveyed Protracted divisions are always aliquot parts but have not been measured by survey. The protraction diagram is a plan of survey.
Z *
Unsurveyed Unprotracted
Unsurveyed Unprotracted divisions are always aliquot parts but there is no survey or plan of survey.  These divisions have been termed extended PLSS or PLSS grids in some implementations.
* The Unsurveyed Protracted and Unsurveyed Unprotracted values reference the survey status or survey condition of a second division.  The second division type for features coded as U or Z is Aliquot Part (A). These values in the domain are included as transitional values and will be eliminated over time.

A typical configuration for the second division in a typical Section 6, the north and west most Section is as shown below.  Most commonly, the corrections for the curvature of the earth and measurement adjustments in the township are accrued into the northern most and western most sixteenth segment, meaning that regular government lotting will be seen on the northern and western boundaries of the township in these cases.

Non-segregation Lots

These lots can be called non-segregating lots, that is, these are government lots created to account for measurement and earth curvature corrections.  Non-segregating or closure government lots can occur along any boundary and even internally within the townships.  They can be found in elongated sections, foreshortened sections, and in many other situations.

The second type of lot is a segregating lot. Segregation is the process of defining lots (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.  In the example below segregation lots are shown against tracts and water.  Tracts and meandered water are non-rectangular PLSS elements and the lots connect or transition the irregular boundaries of the non-rectangular areas to the regular rectangular areas.

Segregation Lots

 Second divisions are rectangular but the government lots may be a bit irregular and government lots may cross the quarter township lines. Also the correct land description of parcels in government lots calls for the Section then the lot number, but not the quarter section designation.  By definition the quarter section is only defined in those parts of the section where there are aliquot parts.  The figure below shows government lots extending over what would be the quarter section lines.

Government lots are numbered uniquely within the section, for the most part.  There are cases of duplicated lot numbers in a section. In these cases the second division suffix is used to distinguish one lot from another, typically with an A for the first occurrence and a B for the repeated occurrence.  In the figure above Lot numbers 7 and 8 are shown as duplicated. The figure below shows a portion of the original 1845 Government Land Office (GLO) Plat (T 4 N R 26 W, 5th PM, Section 1).  

1845 GLO Plat

The PLSS CadNSDI data are a graphical representation and should not be used to replace a survey.  Over time the attribution of the PLSS CadNSDI will improve, but it will not stand in place of a land survey.