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, are 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 Web page. 

    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.     

    The GCDB data is available for download by the public in GIS format from the  GeoCommunicator Land Survey Information System web site. The geographic coordinates representing the GCDB survey-based corners are also available for downloading from GeoCommunicator.  GeoCommunicator also supports  Interactive mapping  and map streaming services of the PLSS data that can be used in your local GIS.