This layer is based on Geographic Coordinate Data Base (GCDB) coordinate data. The locations of Public Land Survey System (PLSS) corners, as represented in geographic coordinate pairs, were derived from a variety of source documents, which include U.S. General Land Office and BLM survey plats/notes, as well as survey data obtained from other U.S. Government agencies, private sector survey firms, and local governments. The attributes assigned to PLSS polygons were taken from the BLM's Legal Land Description (LLD) data set, contained within the Legacy Rehost for the year 2000 (LR2000) automated records system. The coordinate data was produced by using control stations of known location, with varying degrees of accuracy, from various sources which include but are not limited to; U.S. Geological Survey (USGS) topological quadrangles and other sources, National Geodetic Survey (NGS) and US Coast & Geodetic Survey (USC&GS) Cooperative Base Network (CBN) control, Federal Base Network control (FBN), and Continuous Operating Reference Stations (CORS), and Global Positioning System (GPS) data, which is then analyzed and adjusted in concert with official survey data for any given geographic area. The Land Survey Information System Data Base (LSIS) data is a useful representation of the geometry and topology of parcels contained within the PLSS, but its application is intended for mapping purposes only. The GCDB data served from LSIS is not a substitute for a legal land survey.
The GCDB Data was created to provide the BLM and its public with a set of geographic foundation data that accurately portrays the locations of PLSS corners. The GCDB data is based on the best and most current survey records available and uses known geographic positions of control stations within the PLSS network. This data is a key component of the Land Survey Information System (LSIS) framework upon which parcel boundary information will be assembled.
ground condition
The geographic coordinates and their associated products are NOT legal land survey records. The coordinates can NOT be used as a substitute for a legal land survey. They can be used for record keeping, mapping, graphics and planning purposes only. No warranty is made by the Bureau of Land Management for use of the data for purposes not intended by BLM.
P.O. Box 25047
Mail Stop: WO - 330D (DFC)
Building 40, Denver Federal Center
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
100% of the data was checked for attribute accuracy by the GCDB personnel in each of the respective BLM State Offices.
The data set is topologically structured with nodes at all intersections. Labels representing the legal land description are assigned to each land unit.
All GCDB spatial outputs are visually inspected for completeness to ensure that all survey data for a given geographic area is included in the data set.
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 the 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 the 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
Section number
GCDB
Section fractional code. Not used - reserved for future use.
BLM
Full section
BLM
1/4 section
BLM
1/2 section
BLM
3/4 section
BLM
Section duplicate code. Not used - reserved for future use.
BLM
Not duplicate
BLM
First duplicate (second occurance of same section number)
BLM
Second duplicate (Third occurance of same section number).
BLM
Concatenation of section, secfrt, and secdup columns, used to easily join/relate sections and ladesc records.
BLM
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
Spatial representation derived from using record bearings and distances, integrated with geo-referenced positions by an analysis by PCCS or GMM software.
BLM
Spatial representation derived from using record bearings and distances, integrated with geo-referenced positions by an analysis by PCCS or GMM software.
BLM
Spatial representation derived from georeferenced points connected with lines as found on USGS topo map.
BLM
Spatial representation derived from georeferenced points connected with lines as found on USGS topo maps.
BLM
Spatial representation derived from calculations of where the PLSS would be surveyed and monumented.
BLM
Section number used for data labeling purposes.
BLM
Feature geometry.
ESRI
Marks error in data.
BLM
No error in data
BLM
Error in data
BLM
Area of feature in internal units squared.
ESRI
Length of feature in internal units.
ESRI
The LSIS PLSS Land Survey System Township First Division layer (FIRST) contains first division polygons representing surveyed sections.
U.S Department of the Interior, Bureau of Land Management, LSIS Database Description Document other supporting documentation. Internet versions are available at: www.blm.gov/gcdb/standards/index.htm
P. O. Box 25047
WO-330D (DFC)
Building 40, Denver Federal Center
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
Although these data have been processed successfully on a computer system at the U.S Bureau of Land Management, no warranty, expressed or implied, is made by the BLM regarding the utility of the data on any other system, nor shall the act of distribution constitute any such warranty.
P.O. Box 25047
WO - 330D (DFC)
Building 40, Denver Federal Center
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