Geographic Coordinate Data Base (GCDB)


 GPS antennae mounted on two tripods next to an ATV at the top of a hill under a blue sky with mountains in the background (Photo by Ron Schulz/BLM)


BLM is building an automated Land Information System (LIS) for improved public land management.  BLM will use the LIS in making resource management decisions such as processing applications for mineral leases, designating utility corridors, issuing land use permits, locating wildlife habitat improvements, preparing timber sales, evaluating alternatives in environmental assessments and land use plans, and generating reports and maps.

Many types of information, including  the Geographic Coordinate Data Base from the Public Land Survey System, land and mineral records,  natural resource data files, and base maps are being automated for the LIS.  For the first time, the LIS will tie BLM's records and natural resource data to legal descriptions of specific land parcels through a unified automated system.

Fundamental to this approach is the use of a common reference system for the different types of data - namely, a Geographic Coordinate Data Base built from the Public Land Survey System.  The collection, analysis, and management of the data is the responsibility of the Geographic Services Branch of the BLM.


Data Collection

Accurate locations for monuments within a township can be obtained by using a variety of control survey techniques such as a global positioning system.   Other sources of coordinates may also be used to supplement the data base, such as digitizing the location of found corners from various map sources or photographs.  These locations can be used with the bearings and distances of the surveys to calculate latitude and longitude of the remaining corners.  These geographic coordinates may better represent the location of monuments on the ground than the early cadastral survey plats.  Using the concept of an automated Public Land Survey System/Geographic Coordinate Data Base (PLSS/GCDB), survey information that is now manually drawn on maps from separate documents can be shared and displayed automatically on one digital map, with the legal parcel corners as the foundation to which all other information is registered or aligned.

The PLSS/GCDB will eventually contain coordinates for corners of rectangular and special surveys including metes and bounds surveys.  As geographic coordinates are established for resource boundaries, resource data can be merged with the most current land status and survey data because all of the necessary information is located in the same compatible reference system. The diagram below indicates progress in the data collection as of June, 2016.

 Color coded diagram of California with magenta and blue portions covering most of the state (Diagram by J. Leavitt/BLM)


GCDB User's Guide

The GCDB Users' Guide explains the processes used to collect the data.  It explains the GCDB township naming conventions and point identification system.  In addition, there are examples of what some of the files contain that are created during collection.  These files are used for analysis of the data during processing.  Not all files created are included.  The files that are included in this guide contain the data that will be of interest to most users.  Also included is the GMM glossary of terms.

Download GCDB User's Guide


Download GCDB Data

The latest Geographic Coordinate files can be downloaded from the BLM Secure File Transfer Site.  Follow the directions to log onto the site.  The data files for specific townships are located within the meridian directories at the following path: Pub/CA/gcdb.  This data is updated frequently, so keep checking back for current information.

Disclaimer: No warranty is made by the BLM for use of the data for purposes not intended by BLM.