GCDB National Home Page

U.S. DEPARTMENT OF THE INTERIOR

BUREAU OF LAND MANAGEMENT

GCDB



BLM>More BLM Programs>GCDB

Print Page

Geographic Coordinate Data Base (GCDB)

Welcome to the GCDB National Home Page

The Bureau of Land Management (BLM) Geographic Coordinate Data Base (GCDB) is a collection of geographic information representing the Public Land Survey System (PLSS) and some Non-PLSS surveys of the United States. The GCDB grid is computed from BLM survey records (official survey plats and field notes), local survey records and geodetic control information. The GCDB data, combined with PLSS alternate source data, is being used by many Federal agencies, local governments and private companies as the framework for their in-house geographic information system (GIS) systems.

BLM collects the GCDB PLSS data on a township basis. The survey boundaries are delineated by computing the geographic positions of township, section, aliquot part, government lot, and special survey corners. Horizontal control positions from published sources and geographic positioning system (GPS) observations are added and the GCDB grid is adjusted using the least squares method of adjustment to determine the best geographic positions for the survey points. Next, official land descriptions are assigned to each land unit in the grid. The GCDB data are reformatted for use with GIS software, allowing users to view the PLSS information spatially. To find out more about GCDB file formats and data elements go to the GCDB Standards Webpage.

The BLM began collection of the geographic coordinate information in 1989 and the data collection effort continues today. The GCDB Process Diagram (pdf) developed in 1999, graphically depicts how the GCDB data has been collected from official cadastral records, processed to create standardized GCDB flat files and GCDB GIS coverages and electronically posted to the Internet for distribution. GCDB data has been collected for approximately 88% of the townships in the Western United States and the BLM Eastern States Office has collected GCDB for over 1000 townships in Alabama, Arkansas, Louisiana, Michigan, Minnesota, Mississippi, and Missouri.

BLM is now transitioning to collection and maintenance of the GCDB data in the National Integrated Land System (NILS). To date, about 33,000 (97%) of the GCDB townships submitted by the GCDB State Offices have been imported to the NILS Survey Fabric and about 34,000 (99%) of the GCDB townships have been imported to the NILS LD Fabric.

The distribution of GCDB data has already been integrated into NILS. The GCDB data is available for download by the public in GIS shapefile format from the NILS GeoCommunicator Land Survey Information System website. GeoCommunicator also supports live streaming of the NILS PLSS (GCDB and Alternate Source) data. Soon the geographic coordinates representing the GCDB survey-based corners will also be available from GeoCommunicator. Until then, the GCDB coordinates are available to the public in the GCDB flat file and GCDB coverage formats via the National Operations Center (NOC) National Applications “Contact Us” website.

GCDB

Click a link below for:

For additional information or to comment on the GCDB Project, please contact:
Regina_Lefort@blm.gov or Tim_Woods@blm.gov

Some of the documents on this website are pdf files. Therefore, you will need Acrobat Reader to view and print them. To obtain a copy of Acrobat Reader, click the Acrobat Reader link in the Footer at the bottom of this (and all) pages.