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BLM>Colorado>Programs>Geographic Sciences>Cadastral Survey>Geographic Coordinate Data Base
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User's Manual
Published March 14, 1995
Bureau of Land Management
Colorado State Office

Index

INTRODUCTION 
PLSS CORNER IDENTIFICATION 
ONE-QUARTER SECTION CORNER IDENTIFICATION 
ONE-SIXTEENTH SECTION CORNER IDENTIFICATION 
NON-RECTANGULAR SURVEYS IN GCDB 
GMM SECTION 
.RAW-FILE 
.LX-FILE 
.PGC-FILE 
.AN-FILE
GLOSSARY OF ABBREVIATED TERMS

INTRODUCTION

This User's Guide has been compiled in order to give the novice user an introduction to the Geographic Coordinate Data Base (GCDB). The guide manual will familiarize the user with the corner identification used in the output files created by the Public Land Survey System Coordinate Computational System (PCCS) software, and by GCDB Measurement Management (GMM) software, 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 Colorado State BLM Office has the responsibility of producing the GCDB for the State of Colorado. For an up-to-date listing of currently available townships, see the Public Notice posted in the Public Room of the state BLM office. The BLM`s record data contained in the GCDB has been collected with a 98% level of accuracy.

To satisfy the need for more accurate and more complete set of coordinates of the PLSS corners, a system of computer programs, PCCS and GMM have been developed to:

1. Compute the geographic coordinates of PLSS corners using official cadastral survey record data.

2. Provide an estimate of the approximate relative position coordinate dependability.

BLM began the GCDB project using PCCS software and changed to GMM software which is currently being used and will continue to be used in the future to obtain the coordinate values. This software is available for PC's. (486 micro-processor is needed to run the programs.)

At this time, the geographic coordinates are computed using the adjustment of North American Datum 1927 (NAD27).

The data obtained from these computer programs provides the theoretical position of the PLSS corners. The information is used primarily for a Geographic Information System (GIS) type environment to give the relationship of the townships to a point on the earth's surface.

The geographic positions should never be used to replace lost or missing PLSS corners. Refer to the Manual of Surveying Instructions, 1973 for official survey procedures.

PLSS CORNER IDENTIFICATION

GMM utilizes a six digit, fixed length, numerically logical point identIfication code for all PLSS corners.

100700 
 
200700 
 
300700 
 
400700 
 
500700 
 
600700 
 
700700 
100600 
 
200600 
 
300600 
 
400600 
10 
 
500600 
11 
 
600600 
12 
 
700600 
100500 
18 
 
200500 
17 
 
300500 
16 
 
400500 
15 
 
500500 
14 
 
600500 
13 
 
700500 
100400 
19 
 
200400 
20 
 
300400 
21 
 
400400 
22 
 
500400 
23 
 
600400 
24 
 
700400 
100300 
30 
 
200300 
29 
 
300300 
28 
 
400300 
27 
 
500300 
26 
 
600300 
25 
 
700300 
100200 
31 
 
200200 
32 
 
300200 
33 
   
400200 
34 
 
500200 
35 
 
600200 
36 
 
700200 
100100 200100 300100 400100 500100 600100 700100 

The user will note that a grid, of seven North-South, and seven East-West lines, have been constructed. The Prefixes of the North-South lines begin with the number 100, on the western-most line, beginning with section 31, and increase in 100 unit increments as the lines proceed Easterly, to the eastern-most line, which is identified by the Prefix of 700, on the east boundary of section 36. The seven East-West lines begin with a Suffix of 100, at the southern-most line in the township, beginning with sections 31-36, and increase in 100 unit increments, to the northern-most line, which is identified by the Suffix of 700, in sections 1-6.

ONE-QUARTER SECTION CORNER IDENTIFICATION

The previous set of point IDs can be utilized to define the four corners of specific sections within a township, but a further dissection is necessary if PLSS corners are to be identified which were created in the subdivision of sections. The following diagram illustrates the point ID scheme used to identify 1/4 section corners created in the subdivision of a standard section. Section 31 will be used to demonstrate this strategy:
 

 100200 1/4 S 30 
_____ 
S 31 
 200200 
 



              



              
 


              



              
 
1/4 
              

 
100140



              

              
C 1/4 
S 31 
              

 
200140
1/4 
S36 | S31 
 


              



              
140140


              



              
S 31 | S 32 
 


              
100100



              

              

140100



              
200100 
  
1/4 
S 31 
_____ 
S 6 
  

  1. The User will notice that the four 1/4 section corners of section 31, are located at midpoint between respective section corners, and that the 1/4 section corners that fall on the East-West lines are identified with the Prefix 140yyy, while the North-South lines have 1/4 section corners are identifIed by a Suffix of xxx140.

ONE-SIXTEENTH SECTION CORNER IDENTIFICATION

The following diagram illustrates the point ID scheme used to further Identify 1 /16 section corners created in the subdivision of a standard section. Section 31 will be used to demonstrate this strategy: 
 

 W 1/16 S 30 
_____ 
S 31 
E 1/16 S 30 
_____ 
S 31 
 
N 1/16 
S 36 | S 31 
120200


              
               

NW 1/16
S 31 
               

CN 1/16
S 31
               
NE 1/16
S 31
160160
N 1/16 
S 31 | S 32 
100160 
120160


              
               

CW 1/16
S 31
140160


               
               

CE 1/16
S 31
200160 
 
120140


              
               

SW 1/16
S 31 
               

CS 1/16
S 31
160140


               
S 1/16 
S 31 | S 32 
S 1/16 
S 36 | S 31 
120120


              
               


120100
140120


               
               
SE 1/16
S 31
160120
200120 
100120 
W 1/4 
S 31 
_____ 
S 6 

E 1/16 
S 31 
_____ 
S 6 
 

This next division identifies 1/16 section corners, which are located at midpoint between respective 1/4 section corners. Notice that the south 1/16 section corner, on the west boundary of section 31 is Identified with the Prefix of 120yyy. A standard section will identify eight exterior 1/16 sectIon corners, and eight interior 1/16 section corners as illustrated. Further subdivisIon of sections is possible which identifies subdivisional corners subdivided below 1/16 section corners, using this same strategy for point identification.

NON-RECTANGULAR SURVEYS IN GCDB


The previous section dealt with standard rectangular point IDs, but GCDB also identifies PLSS corners which fall outside the rectangular survey system. Non-Rectangular surveys, as the term is used in GCDB, includes meanders, small holding claims, grant boundaries, reservation boundaries, mineral surveys, homestead entry surveys, tracts, etc. These non-rectangular surveys have been broken dawn into four categories:

    1.    Boundaries with Mileposts
    2.    Meanders
    3.    Tracts
    4.    Mineral Surveys, Homestead Entry Surveys (HES) , etc.

The following list identifies (Prefix) point IDs used to describe these non-rectangular surveys:

    1.     711-799 - Boundaries with Mileposts
    2.     800-836 - Meanders
    3.     837-899 - Tracts
    4.     900-999 - Mineral Surveys, Homestead Entry Surveys, etc.

GMM Section

The following list describes the files which are created by the GMM process using the method of Least Squares Analysis and a weighing process based on the year of the survey. Also a brief description of the contents thereof:

 T??SR??W. ___, (i.e., T06SR96W.RAW) 
.RAW Contains point ID's, distance, bearing, and source ID, used to compute coordinates from one point to another within a township. 
 This file is identical with the RxxN/SyyE in PCCS. 
.CON Control available, Cadastral Surveys (BLM), National Geodetic Survey (NGS, formerly U.S. Coast and Geodetic Survey (USC & GS) , U.S. Geological Survey (USGS) Digitized corners from USGS 7' quadrangle maps ) 
 This file is identical with the CxxNSyyE in PCCS. 
.PGC File containing latitude, longitude, reliability and township mean elevation.
 This file is identical with the XxxN/SyyE in PCCS. 
.UTM Final coordinates expressed in Universal Transverse Mercator (UTM) format. (Zone 13 is used for the whole state) 
 This file is identical with the UxxSRyyE in PCCS. 
.DXF AutoCAD file, used for graphics and hard copies using AutoCAD software. 
 These are not stored in with Colorado data but can be generated using the LX2DXF.EXE or LX2DXF utility provided. 

 * Control:

 Control points are allowed to move as much as 1 times the values that they are expected to adjust.

    .001     GPS These control point values do not move in the Least Square Analysis.
         3     Doppler
       10     Convention
       40     Digitized control points from 7' min. USGS quads.
     100     Road intersections

.RAW-FILE (R)

  1. The RawFile contains distance, bearing, and source ID, used to compute coordinates from one point to another within a township.

    SAMPLE Rawfile

      TWP 6S  RNG 96W PM 06     CO             DATE 91/06/11 
    999999 
    100100 100103  8.100 1 2100.0 22272 
    100103 100120  7.130 1 2100.0 22272 
    100120 100123 12.870 1 2100.0 22272 
    100123 100140  7.130 1 2100.0 22272 
    100140 100143 12.620 1 2100.0 22272 <--Source Identifier 
    100143 100160  7.380 1 2100.0 
    100160 100200 20.000 1 2100.0 <-------Bearing (DDMMSS.S) 
    100200 100240 40.000 1 
    100240 100300 40.000 1 <------Quadrant (1=NE 2=SE 3=SW 4=NW) 
    100300 100307 11.420 
    100307 100340 28.580 
    100340 100347  6.150 <------Distance in chains 
    100347 100400 
    100400 100407 <-------TO Point Identifier 
    100407 
    100440 <--------FROM Point Identifier 


    **Example of data entry line 100100:

    "From the cor. of Tps. 43 and 44 N., Rs. 56 W. (100100), N. 021' W., 8.10 chs. dist. to the cor. of Tps.43 and 44 N., R. 57 W. (100103)

    The Source Identifier is a number assigned to a plat of survey.

.LX-FILE

L-file The t-File has PID's, latitude, longitude, mean state elevation, reliability (average and MAXIMUM) and UTM coordinates.

SAMPLE L-FILE

TWP ??N    RNG ??E   PM 06         COLORADO     DATE 92/02/28 
100100 391718.9492 1192029.4353 6000.00 105 243 1 0 2 298054.33 4351208.51 
100120 391732.0948 1192029.5571 6000.00 108 376 1 0 3 298061.90 4351613.88 
100140 391745.2401 1192029.6792 6000.00 108 376 1 0 3 298069.47 4352019.24 
100160 391758.3856 1192029.8010 6000.00 108 376 1 0 3 298077.05 4352424.61 
100200 391811.5310 1192029.9230 6000.00  40  40 1 0 3 298084.63 4352829.98 
100220 391824.4878 1192029.9934 6000.00 108 376 1 0 3 298093.29 4353229.50 
100240 391837.4445 1192030.0640 6000.00 108 376 1 0 3 298101.94 4353629.02 
100260 391850.4013 1192030.1345 6000.00 108 376 1 0 3 298110.61 4354028.54 
100300 391903.3580 1192030.2050 6000.00  40  40 1 0 3 298119.27 4354428.06 
100320 391916.4178 1192030.3637 6000.00 108 376 1 0 3 298125.90 4354830.81 
100340 391929.4775 1192030.5225 6000.00 108 376 1 0 3   |__UTM COORDINATES 
100360 391942.5373 1192030.6812 6000.00 108 376 1 0 3 
100400 391955.5970 1192030.8400 6000.00  40  40 1 0 3 
100420 392008.6386 1192030.7719 6000.00 108 376 1 0 3 
100440 392021.6803 1192030.7038 6000.00 108 376 |_|_|_PEN CODES (GRAPHICS) 
100460 392034.7219 1192030.6356 6000.00 108 376 
100500 392047.7636 1192030.5675 6000.00 108 376 
100520 392100.8052 1192030.4994 6000.00 108 376 
100540 392113.8468 1192030.4313 6000.00  |___|____RELIABILITIES 
100560 392126.8884 1192030.3631 6000.00           average and maximum 
100600 392139.9300 1192030.2950 6000.00 
100620 392152.9847 1192030.1274   |_____PROJECT MEAN ELEVATION 
100640     |___________|________LATITUDE AND LONGITUDE 
100660 
   |________POINT IDENTIFIER 

* Reliability is indicated by two values. The first value is the average distance in feet and the second value is the maximum distance in feet a point adjusted for a particular survey.

Control points in PCCS do not adjust and will have the same average and maximum reliability as shown below.

    1        1    GPS
    3        3    Doppler
  10      10    Conventional control
  30      30    Computed from tri-stations through ties
  40      40    Digitized control points from 71/2 min. USGS quads.
100    100    Digitized control points (Road Intersections)

.PGC - FILE (X)

TWP 060S  RNG 0960 PM 06           CONTROL POINTS      DATE 05/12/94
ORIGIN    393100.0000 1080700.0000 7000.000   0   0 2000.0000 5000.0000
100100    392823.2423 1080931.5117 7000.000  15   8 1819.9166 4759.6475
100103    392828.5239 1080931.5103 7000.000  15   9 1819.9221 4767.7470
100120    392833.1730 1080931.5091 7000.000  15   9 1819.9268 4774.8766
100123    392841.5647 1080931.5055 7000.000  15  10 1819.9372 4787.7457
100140    392846.2139 1080931.5043 7000.000  15  10 1819.9418 4794.8753
100143    392854.4426 1080931.5008 7000.000  15  10    |__Tangent plane
100160    392859.2547 1080931.4996 7000.000  15  10       coordinates
100200    392912.2951 1080931.4907 7000.000   |___|___Reliabilities
100300    393004.4386 1080931.5352 7000.000 
100307    393011.8845 1080931.5393    |______Project Elevation
100340    393030.5167 1080931.5651 
100347         |        | 
100400      Latitude   Longitude
   |____Point identifier

.AN - FILE (LQ)

LQT0060N0960W             05/08/9610:40:01  UTM ZONE = 13
SEC_031 K T_L_8           37.750; M06T0060NR0960W 402518.5800 1081330.3800
SEC_031 J T_L_7           37.660; M06T0060NR0960W      |            |
SEC_031 G T_L_6           37.560; M06T0060NR0960W  Latitude    Longitude
SEC_031 F T_L_5           37.470; M06T0060NR0960W
SEC_030 K T_L_8           37.360;      |____Meridian, Township, Range
SEC_030 J T_L_7           37.250;
SEC_030 G T_L_6              |____Acres
SEC_030 F T_L_5
SEC_031 L T_A |_____Number (Lot, Tract, HES, ...)
SEC_031 I T_A
SEC_031 H   |_____Type (Aliquot, Lot, Tract, ...)
SEC_031 E
SEC_030 |_____Aliquot Location
SEC_030
   |___Section

GLOSSARY OF ABBREVIATED TERMS 

BLM................................................................... Bureau of Land Management 
GCDB................................................................. Geographic Coordinate Data Base 
GIS..................................................................... Geographic Information System 
GMM.................................................................. GCDB Measurement Management 
HES.................................................................... Homestead Entry Survey 
NAD................................................................... North American Datum 
CDOT................................................................. Colorado Department of Transportation 
NGS.................................................................... National Geodetic Survey 
PCCS.................................................................. PLSS Coordinate Computation System 
PID..................................................................... Point Identifier 
PLSS................................................................... Public Land Survey System 
SID..................................................................... Source Identification 
USC & GS.......................................................... U.S. Coast and Geodetic Survey 
USGS.................................................................. U.S. Geological Survey 
UTM................................................................... Universal Transverse Mercator 

Comments about this page should be sent to Paul Lukacovic.