Monday, March 16, 2015

PLSS CadNSDI – PLSS Townships

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


The PLSS Townships are the primary unit of survey for the PLSS, nominally six miles on a side, usually containing 36 sections. PLSS Townships are numbered from base lines and principal meridians. This feature class provides the polygons for the PLSS Townships. The diagram below illustrates the basic PLSS Township referencing and numbering.


A fairly typical set of Townships with their sections is shown below.  The Townships are designated with the Township (Tier) number and direction and the range number and direction.  For example the Township in the middle is Township 30 North Range 31 East.



But to be complete the Townships also need a principal meridian reference.  The list of Principal Meridians (PM) and their national two digit codes are listed at the end of this article.  A map illustrating the principal meridians can be found at this link


A detailed text describing the history and development of each principal meridian and baseline (Initial Points) can be found at this page (Click on Al White for a link to the book).


The attributes for the PLSS Township are listed in the following table.  The field lengths for the attributes may be adjusted in some implementations; this is compliant with the standard intent.  The field names and intended content are the focus of the implementation standard.

PLSS Township Attributes

FieldName
Type
Length
Description
AliasName
STATEABBR
String
2
State abbreviation code two letter postal code
State Abbreviation
PRINMERCD
String
2
Principal meridian code from the BLM PM Code list
Principal Meridian Code
PRINMER
String
40
Principal meridian name as a text
Principal Meridian Text
TWNSHPNO
String
3
Township number. The Township Number indicates the number of rows of townships, north or south from a Public Land Survey System Origin.
Township Number
TWNSHPFRAC
String
1
Township fraction. Township Fractions are created when there are gaps between surveyed Township boundaries or due to excess size in Townships that arose from executing original surveys.
Township Fraction
TWNSHPDIR
String
1
Township direction. The direction of a row of Townships from a Public Land Survey System Origin. These are typically North and South in the West but may be East and West in Ohio
Township Direction
RANGENO
String
3
Range number. The Range Number indicates the number of columns of townships, east or west from a Public Land Survey System Origin.
Range Number
RANGEFRAC
String
1
Range fraction. Range Fractions are created when there are gaps between surveyed Township boundaries or due to excess size in Townships that arose from executing original surveys.
Range Fraction
RANGEDIR
String
1
Range direction. The direction of a column of townships from a Public Land Survey System Origin. These are typically East or West in the west but may be north or south in Ohio
Range Direction
TWNSHPDPCD
String
1
If there are multiple townships in a Public Land Survey System Origin, State and Survey Name, the Township Duplicate Status is used to establish uniqueness. When more than one Public Land Survey System Township has the same Township and Range numbers and directions and fractions, and is in the same State, this attribute is used to distinguish among duplicate values.  A is the first duplicate, B the second etc.  A 0 in this field indicates no duplicates
Township Duplicate
PLSSID
String
50
Concatenation of the principal meridian, township, range, and duplication code that form a unique id.
Township Identifier
TWNSHPLAB
String
20
Township label that is used for cartographic output or web display
Township Label
SRVNAME
String
60
A common or otherwise recognized name for a portion of area of a PLSS Survey, for example the refugee lands in Ohio or in cases where a PLSS Township has a recognized name.
Survey Name for PLSS Areas
SURVTYP
String
2
Code of the type of special survey, typically these are the codes described in the BLM data collection as survey type codes
Survey Type Code
SURVTYPTXT
String
50
Special survey type text description, for interpreting the codes
Survey Type Text
SOURCEDATE
Date
8
The date of the source document
Source Date
SOURCEREF
String
100
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

Why is the state included in the PLSS Township Table?  This is because in some cases, notably along the Colorado-Kansas boundary, the Principal Meridian, numbers and directions for two “columns” of townships are repeated, with the only unique designation being the state.  Also many state boundaries in the west are coincident with Township boundaries.  Townships that are split by state lines are divided into two polygons for the standardized data.

The survey type is used to identify unsurveyed townships and townships that have been defined on a protraction diagram, which is a plan of survey.  If the survey type is blank, the township boundary has been surveyed.  The source date and source reference are optional fields that can be used to identify the first date of survey and the source document, typically a General Land Office (GLO) or BLM plat.

The figure below illustrates some fractional or half township and half ranges in Nevada. Fractional parts can be half, quarter, or three quarters.  Fractional townships may not be familiar to many of the PLSS data users, but they occur in almost every state.



The other exceptional coding are the duplicate townships.  This happens when the Township tier, range, and PM are duplicated within a state.

The image below is from a portion of the Ohio PLSS from the Ohio River Base PM.  The Township labels have the duplicate code at the end.  The first duplicate has an A indicating that another Township with the same designation exists.  The convention is to assign the first duplicate code, A, to the township closest to the baseline or PM.


The Principal Meridians included in the PLSS CadNSDI standardized data are listed.

Principal Meridians

Principal Meridian Code
Principal Meridian Description
01
1st Meridian
02
2nd Meridian
03
3rd Meridian
04
4th Meridian
05
5th Meridian
06
6th Meridian
07
Black Hills Meridian
08
Boise Meridian
09
Chickasaw Meridian
10
Choctaw Meridian
11
Cimarron Meridian
12
Copper River Meridian
13
Fairbanks Meridian
14
Gila-Salt River Meridian
15
Humboldt Meridian
16
Huntsville Meridian
17
Indian Meridian
18
Louisiana Meridian
19
Michigan Meridian
20
Montana Meridian
21
Mount Diablo Meridian
22
Navajo Meridian
23
New Mexico Meridian
24
St. Helena Meridian
25
St. Stephens Meridian
26
Salt Lake Meridian
27
San Bernardino Meridian
28
Seward Meridian
29
Tallahassee Meridian
30
Uintah Meridian
31
Ute Meridian
32
Washington Meridian
33
Willamette Meridian
34
Wind River Meridian
36
Between the Miamis
37
Muskingum River
38
Ohio River Base
44
Kateel River Meridian
45
Umiat Meridian
46
Extended Fourth Meridian
47
West of the Great Miami
48
Base Line of the US Military Survey
99
Not Applicable


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