BLM Geographic Coordinate Data Base (GCDB)


The GCDB in a Nutshell

    The Bureau of Land Management (BLM) maintains a collection of geographic information representing the United States Public Land Survey System (PLSS) and other official surveys. This GCDB (Geographic Coordinate Data Base) data is computed from BLM’s official survey records including Cadastral survey plats and field notes supplemented with local survey records and geodetic control information. The GCDB data is available via the Internet in geographic information system (GIS) formats and during the last few years geospatial products like the Cadastral National Spatial Data Infrastructure (CADNSDI) file geodatabases have become distributed on-line.


The best positions for these survey points in the GCDB are determined by:
  • Collecting the locations of all township, section, aliquot part, government lot and special survey corners in a township,
  • Incorporating horizontal control positions from published sources and GPS observations to tie the survey framework to the earth,
  • Adjusting the GCDB using the least squares method of adjustment to determine the best geographic positions for all of the survey points in the dataset,
  • Assigning the official land descriptions to every land unit depicted in the GCDB,
  • Translating the resulting framework into GIS formats for use with spatial applications.

    CADNSDI file geodatabases for Arizona, California, Colorado, Idaho, Montana/North Dakota, Nevada, New Mexico, Utah and Wyoming are available for download from the PLSS Data Download site on the GeoCommunicator Download Public Land Survey System (PLSS) Data web site with databases for Oregon and Washington expected to be available soon. 

GEODATABASE INFORMATION
Formats: ESRI ArcGIS 9.3 CadNSDI PLSS-File GeoDatabase
Legacy PLSS-Shapefile Format
Projection: Geographic(GCS) NAD83 Datum
Metadata: Embedded for CadNSDI PLSS format
See Metadata page for Legacy Metadata and a sample of the CadNSDI metadata




ACCESS TO GCDB DATA VIA GEOCOMUNICATOR:

PLSS DATA DOWNLOAD
New CadNSDI PLSS Data Download
Complete Statewide file geodatabase
with embedded metadata

Legacy PLSS Data Download by state or by individual county shapefile
Continue to use the LSIS Map Viewer to download individual townships and to export Geographic Coordinate Database (GCDB) points and lines
Last updated Dec. 2009
Metadata

Select 'BLM FGDB' to download
Select 'Source Data" file (BLM or Alt) to download State data or select "County Download" to go to the County selection
State
BLM File GDB
last updated
Sample Metadata
State BLM GCDB Shapefile
State Alt Source Shapefile
Download By County
Alabama
 
 
 
Alaska  
 
Arizona
BLM FGDB
04/11/2011
Arkansas
 
 
California
BLM FGDB
09/19/2011
Colorado
BLM FGDB
04/11/2011
Florida
 
 
Iowa
 
 
 
Idaho
BLM FGDB
04/11/2011
Illinois
 
 
 
Indiana
 
 
 
Kansas
 
 
Louisiana
 
 
Michigan
 
 
Minnesota
 
 
Mississippi
 
 
Missouri
 
 
Montana/ND
BLM FGDB
(Hosted with State of MT)




Nebraska
 
 
Nevada
BLM FGDB
04/11/2011
New Mexico
BLM FGDB
04/11/2011
North
Dakota/MT
BLM FGDB
04/11/2011
Ohio
 
 
 
Oklahoma
 
 
Oregon
 
 
South Dakota
 
 
Utah
BLM FGDB
04/11/2011
Washington
 
 
West Virginia
 
 
 
Wisconsin
 
 
 
Wyoming
BLM FGDB
04/11/2011

PLSS Map Services (map and feature) in Legacy Format only:
ArcIMS: Server: http://www.geocommunicator.gov, Service Name: BLM_MAP_PLSS, BLM_FEATURE_PLSS
WMS: http://www.geocommunicator.gov/wmsconnector/com.esri.wms.Esrimap?ServiceName=BLM_MAP_PLSS
ArcGIS (REST, SOAP, WMS, KML) http://www.geocommunicator.gov/ArcGIS/rest/services/PLSS/MapServer




Legacy PLSS Information

Datum: All data is in NAD83 Datum
Geographic transformation for data in NAD27 to NAD83 used "GCS_NAD_27 to GCS_NAD_83_NADCON" for conversion
Projection: Geographic Coordinates 
Unit of Measurement: Decimal Degrees 
Legacy PLSS Metadata
CadNSDI Data Schema Mapping: Overview and crosswalk of legacy PLSS formats to CadNSDI PLSS formats (doc, pdf)

    The PLSS shapefiles are created from the BLM cadastral surveys. The GCDB data is collected from the original BLM survey and resurvey records (official plats and field notes), local survey records, and geodetic control information. Once the record PLSS corner positions are collected, the resulting framework is adjusted using weighted least squares adjustment processes to determine the best estimation of the original corner positions.  The records are then reformatted so Geographic Information System (GIS) software can be used to view the PLSS information spatially. Note that the BLM GCDB coordinates are generally the best PLSS source data (where it has been collected).  However, the GCDB coordinates are meant for uses like map-making and determining search areas for locating PLSS corners on the ground.  The GCDB coordinates are NOT to be used to establish (or reestablish) PLSS corner positions on the ground.

    The Alternate Source data has been collected to various standards.  This dataset usually contains only section subdivisions (section center-lines and sixteenth lines) where these subdivisions have been needed by BLM to delineate Federal interest lands. BLM makes no judgment as to the quality and accuracy of the non-BLM data.

    The GeoCommunicator website supports interactive viewing and streaming (ArcIMS, ArcGIS, WMS) of the legacy PLSS data. The data is displayed to the lowest level that was collected including sections, aliquots, and special surveys. This data provides the foundation for most land-based geographic information systems.

GCDB flat files are ASCII files that are not formatted to be used with GIS software. The GCDB flat files in Standard File format are currently available on request for all townships depicted in gold on the LSIS Data Download Availability map.  The datum for the flat files is NAD27.  To request the Flat Files contact the GCDB Manager with jurisdiction for the state where the PLSS data is located.

For information on the GCDB project, contacts and standards visit the project Web site at http://www.blm.gov/wo/st/en/prog/more/gcdb.html.
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