A GUIDE TO INTERPRETING THE
GEOGRAPHIC COORDINATE DATA BASE (GCDB)
This User's Guide has been compiled in order to give the novice user an introduction to corner identification used in the Geographic Coordinate Data Base (GCDB) and to familiarize the user with the output files created by the Public Land Survey System (PLSS), the Geographic Measurement Management (GMM), and their functionality.
The GCDB has been developed in order to render the most dependable coordinates available for the U.S. Public Land Survey System (PLSS) corners. The Montana State Office is responsible for producing the GCDB for North Dakota, South Dakota and Montana. At present, portions of Montana and North Dakota have been produced, but a collection plan for South Dakota has yet to be compiled. The data contained in the GCDB has been collected with a 98% level of accuracy.
To satisfy the need for an accurate and complete set of coordinates of PLSS corners, a system of computer programs, GMM, has been utilized to:
- Compute the geographic coordinates of PLSS corners using official cadastral survey record data.
- Provide an estimate of the approximate relative position coordinate dependability. Where State Plane Coordinates (SPC) are used, the coordinates and associated reliability are expressed in feet. GCDB also produces Universal Transverse Mercator (UTM) coordinates, stored in the .UTM file. The coordinates and their reliability are in meters. They are not a reflection of true (absolute) coordinate reliability but rather reflect the integrity of the survey information used.
The geographic coordinates and their by-products were generated from either Public Land Survey System Coordinate Computational Software (PCCS) or geographic coordinate data base measurement management (GMM) software using official Public Land Survey System (PLSS) records (and when deemed necessary, state, county, and private survey records) or digitized coordinates from various cartographic and photographic products. Except where a corner monument has been used as a first or second order control point and the results are of public record, the coordinate values used by GCDB are established with varying reliability based on the source material and method of data input. These coordinate values will be updated as better data and methodology are available. Graphic representations using these values depict the most probable township configuration and may change as a result of such updates. The geographic coordinates and their associated products have NO legal significance. These coordinates cannot be used as a substitute for a legal boundary survey. They can be used for recordkeeping, 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.
GCDB Data Access Procedures
- The preferred method of obtaining GCDB data is via this website.
- Alternatively, data can be obtained through the BLM Public Room. There is a nominal charge for data obtained this way to cover the cost of the medium and expenses.
Typical procedure for Public Room requests:
1. Members of the public ask the Public Room for GCDB data by township and range.
2. Provide customer with this GCDB user guide.
3. After determining the necessary data being requested, either hard copy or diskette of GCDB data, the public room employee will phone GCDB section.
4. Public room staff will tell GCDB personnel which files on what medium (diskette, paper copy or tape) are wanted and wait while GCDB personnel check the availability and size of requested information.
5. GCDB personnel will supply the Public Room employee with the number of pages to be printed for hard copy requests such as manuals or printed data. The cost of digital data for computers is $8.00 administrative fee, plus research time at $18.60/hr., plus the cost of the media (diskette, tape, CD-ROM), plus postage. The Public Room is responsible for billing and collecting these fees. The Public Room will accept VISA and MasterCard and phone orders. No data will be released before payment has been made. GCDB is responsible for assuring that the data is wanted at the established rates. For walk-in requests, the Public Room staff out Form 1370-44 for cost recovery and will have the customer pay for the requested information at the cashier's window.