Public Land Survey System Township (twnshp)

For information about the data content, please contact the BLM State Office, GCDB Manager or GCDB Contact at: http://www.blm.gov/gcdb/gcdbsites/index.html

For information directly relating to metadata, please contact Regina LeFort at regina.lefort@blm.gov

Accuracy of the individual points contained within the GCDB layers of LSIS that were determined using GMM software  were adjusted using both compass rule and a least squares analysis, which examines the geometry of PLSS parcels in relation to the coordinate values of known locations for control points within the PLSS grid.  Each individual point carries a reliablility factor indicating the error ellipse in both northing and easting which is reported after the least squares analysis is completed.



Accuracy of the individual points contained within the GCDB layers of LSIS that were determined using PCCS software  were adjusted using a succession of compass rule adjustments between the control points followed by a least squares analysis, which examines the geometry of PLSS parcels in relation to the coordinate values of known locations for control points within the PLSS grid.  Each individual point carries positional reliability factors for the average of the misclosures in the data set and the maximum misclosure in the data set.

Survey data in the form of official (microfilm, CD, other) survey and BLM, abstracted into a vector digital format.

Survey and control data from the Cartographic Feature File (CFF) data set.

Digitized control data from standard topological quadrangle sheets.

Survey control data from the official control station sheets (CBN, FBN, CORS).

Compile survey input data from the best and most current survey records.

Compile listings of known locations of PLSS corners.

Coordinates of control stations are entered into a control data base with associated reliabilities.

This data has been created in either GMM or PCCS format. The following process steps refer to data in GMM format.



With GMM survey data, abstracted from survey plats, and control stations extracted from the control database, are manually entered with weighting factors into GMM software.  Compass rule and least squares adjustments are performed using weighting factors assigned to both control stations and survey line data, based on methodologies and vintage of survey.



With GMM, section subdivision is performed to achieve land unit detail to at least the forty acre parcel level.  Instructions for calculating non-regular and minor subdivisions are persistently stored during collection and rerun after every new adjustment in order to achieve the detail necessary to delineate all lines required for depicting federal rights, interestes, restrictions, and encumberances.  Coincident lines and lines identified as non-boundary lines are removed from the data set used for final land unit constructions.  Line intersections are computed and given unique identifiers and  land units are constructed.



GMM lists all coordinates produced by the compass rule and least squares adjustments and subdivision, with conectivity codes between points and compiles them into a single file for development of Geographic Information Systems (GIS) output.

This data has been created in either GMM or PCCS format. The following process steps refer to data in PCCS format.



With PCCS, survey data abstracted from survey plats and control stations extracted from control data base are manually entered into the PCCS processing software.  A succession of compass rule adjustments is performed on the lines to adjust them to the control points, followed by a least squares analysis.  The resulting coordinates are accompanied by indications of positional reliability; the average of misclosures in the data set and the maximum misclosure in the data set.



PCCS lists all coordinates produced by the compass rule and least squares adjustments with conectivity codes between points and compiles them into a single file for development of GIS files.



With PCCS, section subdivision is performed to achieve land unit detail to at least the forty acre parcel level.

GCDB data conversion software verifies correctness of GCDB file formats and content.

Verified coordinate, line and label files are converted to GIS coverages using the topology check application.  All errors in topology are flagged for editing and correction.

If topological errors exist, editing of arc and node data, as well as parcel labels, is performed using either GMM or ArcInfo Interface (AII).  (PCCS townships can only be edited using AII).  Final edits are entered into input files and the process is repeated until all errors are corrected and a successful GIS coverage is created.

GIS coverages are edgematched with adjoining township data sets to insure a seamless PLSS grid is created.

Topologically correct GIS coverages are modified to use FGDC compliant naming conventions and then loaded into the LSIS database.  These layers can then be downloaded as shapefiles through the LSIS website.

Metadata imported.

Internal feature number.

ESRI

A unique identifier for each township. The lndkey is read: State, Prime Meridian, Township (including fractions and direction), and range (including fractions and direction). Ex: ST00T0000N0000E. The numbers directly before the direction  indicate if a township or range is fractional. See attributes twnfrt and rngfrt for values and definitions of the fractions.

BLM

Numeric code identifying range number.

BLM

Alpha code for identifying direction of township.

BLM

Numeric code identifying fractional range.

BLM

Alpha code for determining a duplicate township.

BLM

Principal Meridian

BLM

2 Letter State Abbreviation

BLM

Feature geometry.

ESRI

Agency in FGDC CDCS model that provided data. An agent is an individual, organization, or public agency that holds rights, interests, or restricitions in land, holds or files land records, or has established a land description, a coordinate value or a monument.

FGDC

Date this feature updated within NILS

BLM

Township/range columns concatenated for map labeling purposes.

BLM

Numeric code identifying tier number.

BLM

Numeric code identifying fractional tier

BLM

Alpha code for identifying direction of township.

BLM

Marks error in data

BLM

Not used

BLM

Area of feature in internal units squared.

ESRI

Length of feature in internal units.

ESRI

For information about the data content, please contact the BLM State Office, GCDB Manager or GCDB Contact at: http://www.blm.gov/gcdb/gcdbsites/index.html

For information directly relating to metadata, please contact Regina LeFort at regina.lefort@blm.gov

For information about the data content, please contact the BLM State Office, GCDB Manager or GCDB Contact at: http://www.blm.gov/gcdb/gcdbsites/index.html

For information directly relating to metadata, please contact Regina LeFort at regina.lefort@blm.gov