twpgrid
Identification_Information
Data_Quality_Information
Spatial_Data_Organization_Information
Spatial_Reference_Information
Entity_and_Attribute_Information
Distribution_Information
Metadata_Reference_Information
Identification Information
Section Index
Citation:
Citation Information:
Originator: U.S. Dept. of Interior, Bureau of Land Management, Division of Cadastral Survey and Geomatics, Branch of Spatial Records
Publication Date: 2001
Title: twpgrid
Geospatial Data Presentation Form: vector digital data
Online Linkage: ftp://agdcftp1.wr.usgs.gov/pub/blm/sdms
Description:
Abstract:
Township boundaries were generated from geodetic latitude and longitude coordinate pairs as recorded on BLM's official protraction diagrams of the state of Alaska. The township coverage identifes 18,654 townships as 18,658 polygons (four townships require two polygons each), as depicted on the official BLM protraction diagrams. TWPGRID is a double precision geodetic Arc/Info coverage available in both an Arc/Info Export coverage and ESRI shape file format.
Purpose:
For GIS mapping and analytical use. This double precision coverage precisely maps the township coordinates as defined on the official BLM protraction diagrams. Not for use in determining area computations. Please consult official BLM protraction diagrams for the record protracted area.
Supplemental Information:
The values used for this data were initially obtained from U.S., Department of the Interior, Bureau of Land Management, Alaska State Office, Division of Cadastral Survey and Geomatics's (BLM) AEH (acronym unknown) coordinate files.
These files represented townships in two ways as follows:
1. Regular Townships were represented as a geodetic rectangle bounded by two latitudes and two longitudes.
2. Irregular Townships were represented as a sequential series of geodetic coordinate pairs.
Additionally these files represented township subdivision by recording the origin point for township's subdivision as a code for one of the four township's corners and a series of codes indicating which rows and columns of sections were intended to be created. Collectively these codes are referred to as "shape codes."
In 1996 BLM obtained an updated version of the AEH files from the State of Alaska, Department of Natural Resources (ADNR.)
A comparison was performed between the most current set of BLM's files and ADNR's files. Lists of differences were compiled and resolved as follows:
1. Additional Townships
The additional townships shown in ADNR's files were discarded as they represent marine townships and their creation and maintenance is not the responsibility of the BLM.
One additional township shown in BLM's files was discarded as it represented land shown in another township that was properly represented.
2. Subdivision Shape Code Differences
Referring to the official protraction diagrams the proper shape codes were utilized.
Subdivision shape codes are implied on the official protraction diagrams as the township's graphic representation through the use of parenthetical distances.
3. OrthogonalTownship Boundary Position Differences Shown On Official Protraction Diagrams
Referring to the official protraction diagrams the proper positions were utilized.
Orthogonal township boundaries are shown on the official protraction diagrams as lines of true-mean-bearing along meridians of longitude and parallels of latitude. Reported on these diagrams are geodetic coordinates for the latitude and longitude for these lines. These coordinates are reported on the North American Datum 1927 (NAD27.)
4. Orthogonal Township Boundary Position Differences Not Shown On Official Protraction Diagrams
Referring to the official protraction diagrams the proper positions were calculated and utilized.
These positions were rounded to the nearest 1/1000 of a second for compatibility with adjacent townships.
5. L-shaped Irregular Townships
These townships are "puzzle pieces" used along the intersection of meridians or for certain correctional meridians and/or parallels shown on the official protraction diagrams.
No differences were noted between the two sets of files.
6. Alaskan-Canadian Irregular Townships
Referring to the official protraction diagrams it was noted that neither BLM's or ADNR's files appeared to properly represent these townships. Therefore it was necessary to recompile these townships.
Initially the townships represented in this manner were restricted to a portion along the international boundary in the southeastern panhandle of the State, specifically from the head of Tongass Passage to Mount St. Elias.
Referring to the U.S., Department of State, International Boundary Commission (IBC) publication "JOINT REPORT UPON THE SURVEY AND DEMARCATION OF THE BOUNDARY BETWEEN CANADA AND THE UNITED STATES FROM TONGASS PASSAGE TO MOUNT ST. ELIAS, 1952" (IBC 1952) it was decided to represent those townships from the mouth of Tongass Passage to it's head as irregular townships.
Further it was noted that Boundary Point 187 at the northern end of this portion of the international boundary recorded in the IBC 1952 publication was not on the 141st meridian. Referring to the IBC publication "JOINT REPORT UPON THE SURVEY AND DEMARCATION OF THE INTERNATIONAL BOUNDARY BETWEEN THE UNITED STATES AND CANADA ALONG THE 141ST MERIDIAN FROM THE ARCTIC OCEAN TO MOUNT ST. ELIAS, 1918" (IBC 1918) it was noted that the 141st meridian portion of the international boundary was recorded on the Yukon Datum at 141 degrees West longitude.
Therefore it became necessary to additionally represent all of the townships along the 141st meridian as irregular townships.
For the "southeastern" portion of the Alaskan-Canadian boundary (not including Boundary Point 187) the coordinate values used are reported in the IBC 1952 publication. These coordinates are reported on the North American Datum 1927 (NAD27.)
For the "141st Meridian" portion of the Alaskan-Canadian boundary (including Boundary Point 187) the coordinate values reported in IBC 1918 publication are on the Yukon Datum. In order to get proper coordinates BLM contacted the IBC and a list of coordinates was obtained. These coordinates were reported on the National Geodetic Reference Datum of 1983 (NAD83.) These coordinates were further processed using the U.S., Department of Commerce, National Oceanic and Atmospheric Administration, National Geodetic Survey (NGS) computer program NADCON version 2.1 to obtain NAD27 coordinates.
Intersections of the orthogonal township boundaries (true-mean-bearing) and the Alaskan-Canadian boundary (line-of-sight) were then computed and irregular townships were then constructed from the results.
This process showed that one township adjacent to Tongass Passage, that had been represented as an orthogonal township falls completely in Canada. That township was discarded.
Upon completion of this process GIS techniques were used to confirm that proper topology existed in this data.
This process showed that in three localities a small parcel of land was shown in two townships. Referring to the official protraction diagrams it was decided to amend three of these diagrams and to construct three additional irregular townships.
Additional analysis with BLM's Alaska Land Information System (ALIS) showed that a township had been surveyed that was not represented in this data. That township was added to this data as an orthogonal township.
Time Period of Content:
Time Period Information:
Currentness Reference: publication date
Status:
Progress: Complete
Maintenance and Update Frequency: As needed
Spatial Domain:
Bounding Coordinates:
West Bounding Coordinate: -187.568381
East Bounding Coordinate: -129.972243
North Bounding Coordinate: 71.468618
South Bounding Coordinate: 51.202992
Keywords:
Theme:
Theme Keyword Thesaurus: None
Theme Keyword: township
Theme Keyword: range
Theme Keyword: twps
Theme Keyword: mtr
Theme Keyword: meridian
Theme Keyword: protraction
Theme Keyword: plss
Theme Keyword: survey
Theme Keyword: rectangular
Place:
Place Keyword Thesaurus: none
Place Keyword: Alaska
Access Constraints: To ensure distribution of the most current public information, please refer requests for data to the Branch of Spatial Records.
Use Constraints:
Accuracy published on or derived from the official BLM township protraction diagrams. Any hardcopies or published datasets using this data shall clearly indicate their source.
Any users wishing to modify this data are obligated to report the extent of their modifications. User specifically agrees not to misrepresent modifications to this data, as approved or endorsed by the BLM.
Any discrepancies or errors in this data should be reported to BLM
Point of Contact:
Contact Information:
Contact Person Primary:
Contact Person: Tom Deiling, Chief, Branch of Spatial Records
Contact Organization: Division of Cadastral Survey and Geomatics, Branch of Spatial Records
Contact Position: Chief Branch of Spatial Records
Contact Address:
Address Type: mailing address
Address: 222 W. 7th Ave. #13
City: Anchorage
State or Province: AK
Postal Code: 99513
Country: USA
Contact Voice Telephone: 9072713797
Contact Facsimile Telephone: 9072714549
Contact Electronic Mail Address: Tom_Deiling@ak.blm.gov
Hours of Service: 0800-1630
Browse Graphic:
Data Set Credit: BLM Official Protraction Diagrams; International Boundary Commission for Alaska/Canadian Boundary; ADNR for ongoing coordination
Native Data Set Environment: AIX 4.3.3 ; ESRI UNIX Arc Version 7.2.1 Patch 2-
Data Quality Information
Section Index
Attribute Accuracy:
Attribute Accuracy Report:
Attributes assigned to this coverage are defined in the Informix tables. The twpgrid coverage is joined to the Informix tables by means of a unique identifier.
Attributes are extracted from the Informix tables and joined with the coverage features to ensure referential integrtity with the database. Spot checks were performed to verify attribute accuracy.
Logical Consistency Report: Polygon topology is present. No intersection errors or label errors are present.
Completeness Report: There is a one-to-one relationship between each township in the spatial database and on the offical protraction diagrams
Positional Accuracy:
Horizontal Positional Accuracy:
Horizontal Positional Accuracy Report:
The accuracy of the coordinates in this data is absolute due to their theoretical nature, however the source data shows values to the nearest fraction of a second of latitude or longitude as follows:
1. Township Corners:
0.001" as shown on or calculated from official protraction diagrams, except Umiat Meridian latitudes where they are 0.01".
2. Section Corners:
0.00001" as calculated to preserve angularity and distance.
3. Points along Alaskan-Canadian Boundaries:
3a. For points between Tongass Passage and Mt. St. Elias (not including Boundary Point 187), 0.01" as shown in U.S. Department of State, International Boundary Commission (IBC) publication "JOINT REPORT UPON THE SURVEY AND DEMARCATION OF THE BOUNDARY BETWEEN CANADA AND THE UNITED STATES FROM TONGASS PASSAGE TO MOUNT ST. ELIAS, 1952."
3b. For points between Mt. St. Elias and the Arctic Ocean (including Boundary Point 187), 0.00001" to preserve backwards compatibility with National Geodetic Reference Datum of 1983 using U.S., Department of Commerce, National Geodetic Survey (NGS) computer program NADCON version 2.1.
3c. For intersection points of orthogonal township boundaries with the Alaskan-Canadian boundaries, 0.00001" as calculated to preserve angularity and distance.
Vertical Positional Accuracy:
Vertical Positional Accuracy Report: unknown
Lineage:
Process Step:
Process Description:
Coordinate and attribute information extracted from SQL Query from Informix database. Refer to the abstract and supplemental information regarding coordinate information.
1. Construct ESRI Arc/Info coverage generate file from SQL Query of the informix database.
2. Construct Arc/Info coverage and topology with Arc/Info BUILD command
3. Verify no unlabeled polygons, mulitple label polygons, or intersecting arcs exist.
4. Define projection as:
projection geographic
units decimal degrees
Datum NAD27
paramenters
5. Join attributes from Informix township table to coverage
6. Densify arcs at 0.027 decimal degrees (provides 6 intersections on east-west township lines that are coincident with the section coverage.
Process Date: 20010214
Process Contact:
Contact Information:
Contact Person Primary:
Contact Person: Tim Varner
Contact Organization: Bureau of Land Management, Alaska State Office, Division of Cadastral Survey and Geomatics, Branch of Spatial Records
Contact Position: Spatial Database Administrator
Contact Address:
Address Type: mailing address
Address: 222 W. 7th Ave. #13
City: Anchorage
State or Province: AK
Postal Code: 99513
Country: USA
Contact Voice Telephone: 907-271-5799
Contact Facsimile Telephone: 907-271-4549
Contact Electronic Mail Address: Tim_Varner@ak.blm.gov
Hours of Service: 0800-1630
Spatial Data Organization Information
Section Index
Direct Spatial Reference Method: Vector
Point and Vector Object Information:
SDTS Terms Description:
SDTS Point and Vector Object Type: Complete chain
Point and Vector Object Count: 43776
SDTS Terms Description:
SDTS Point and Vector Object Type: Label point
Point and Vector Object Count: 18658
SDTS Terms Description:
SDTS Point and Vector Object Type: GT-polygon composed of chains
Point and Vector Object Count: 18685
SDTS Terms Description:
SDTS Point and Vector Object Type: Point
Point and Vector Object Count: 4
Spatial Reference Information
Section Index
Horizontal Coordinate System Definition:
Geographic:
Latitude Resolution: 0.000027778
Longitude Resolution: 0.000027778
Geographic Coordinate Units: Decimal degrees
Geodetic Model:
Horizontal Datum Name: North American Datum of 1927
Ellipsoid Name: Clarke 1866
Semi-major Axis: 6378206
Denominator of Flattening Ratio: 294.9786982
Entity and Attribute Information
Section Index
Detailed Description:
Entity Type:
Entity Type Label: twpgrid.pat
Attribute:
Attribute Label: MERIDIAN
Attribute Definition: Meridian-township-range, township and range values have leading zeros as place holders
Attribute Definition Source: BLM official protraction diagrams
Attribute Domain Values:
Enumerated Domain:
Enumerated Domain Value: S
Enumerated Domain Value Definition: Seward Meridian
Enumerated Domain Value Definition Source: BLM official protraction diagrams
Enumerated Domain Value: C
Enumerated Domain Value Definition: Copper River Meridian
Enumerated Domain Value Definition Source: BLM official protraction diagrams
Enumerated Domain Value: F
Enumerated Domain Value Definition: Fairbanks Meridian
Enumerated Domain Value Definition Source: BLM official protraction diagrams
Enumerated Domain Value: K
Enumerated Domain Value Definition: Kateel River Meridian
Enumerated Domain Value Definition Source: BLM official protraction diagrams
Enumerated Domain Value: K
Enumerated Domain Value Definition: Kateel River Meridian
Enumerated Domain Value Definition Source: BLM official protraction diagrams
Enumerated Domain Value: U
Enumerated Domain Value Definition: Umiat Meridian
Enumerated Domain Value Definition Source: BLM official protraction diagrams
Attribute:
Attribute Label: MTR
Attribute Definition: Meridian-Township-Range with leading zeros as placeholders
Attribute Definition Source: BLM official protraction diagrams
Attribute Domain Values:
Unrepresentable Domain: There are five meridians: S (seward), C (copper river), F (fairbanks), K (kateel river), U (umiat)
Attribute:
Attribute Label: RNG
Attribute Definition: Number township is east or west of a principal meridian
Attribute Definition Source: BLM official protraction diagrams
Attribute Domain Values:
Range Domain:
Range Domain Minimum: 001
Range Domain Maximum: 266
Attribute:
Attribute Label: RNG_DIR
Attribute Definition: Township East/West direction. Indicates whether the township is East or West of the principal meridian.
Attribute Definition Source: BLM official protraction diagrams
Attribute Domain Values:
Unrepresentable Domain: East or West
Enumerated Domain:
Enumerated Domain Value: E
Enumerated Domain Value Definition: East
Enumerated Domain Value: W
Enumerated Domain Value Definition: West
Attribute:
Attribute Label: RNG_FRAC
Attribute Definition: Fractional range. Represented as 0 or 2 in the rng_frac field. Represented as .5 as concatenated in the mtr field.
Attribute Definition Source: BLM official protraction diagrams
Attribute Domain Values:
Enumerated Domain:
Enumerated Domain Value: 0 or 2
Enumerated Domain Value Definition:
0 indicates this is not a fractional township.
2 indicates this is a fractional township
Unrepresentable Domain:
Represented as 0 or 2 in the rng_frac field. Fractional ranges are represented as .5 in the mtr field.
There are ten (10) fractional ranges: C017S11.5E; C018S11.5E; C019S11.5E; C020S11.5E; C021S11.5E; C019S27.5E; C020S27.5E; C034S48.5E; C035S48.5E; C036S48.5E
Attribute:
Attribute Label: TWP
Attribute Definition: Number township is north or south of a meridional baseline
Attribute Definition Source: BLM official protraction diagrams
Attribute Domain Values:
Range Domain:
Range Domain Minimum: 001
Range Domain Maximum: 103
Attribute:
Attribute Label: TWP_DIR
Attribute Definition: Township North/South direction. Indicates whether the township is North or South of the meridional baseline.
Attribute Definition Source: BLM official protraction diagrams
Attribute Domain Values:
Unrepresentable Domain: North or South
Enumerated Domain:
Enumerated Domain Value: N
Enumerated Domain Value Definition: North
Enumerated Domain Value: S
Enumerated Domain Value Definition: South
Attribute:
Attribute Label: TWP_FRAC
Attribute Definition: Fractional township. Represented as 0 or 2 in the twp_frac field. Represented as .5 as concatenated in the mtr field.
Attribute Definition Source: BLM official protraction diagram
Attribute Domain Values:
Enumerated Domain:
Enumerated Domain Value: 0 or 2
Enumerated Domain Value Definition:
0 indicates this is not a fractional township.
2 indicates this is a fractional township
Unrepresentable Domain:
Represented as 0 or 2 in the twp_frac field. Fractional townships are represented as .5 in the mtr field.
There are four (4) fractional townships: C036.5S045E; C036.5S046E; C036.5S047E; C036.5S048E
Range Domain:
Range Domain Minimum: 0
Range Domain Maximum: 2
Attribute:
Attribute Label: TWP_TIN_NO
Attribute Definition: BLM-Five digit township index number.
Attribute Definition Source: BLM official protraction diagrams
Attribute Domain Values:
Unrepresentable Domain:
1-21,200 Distributed by meridian and quadrant of that meridian:
1-598 C-NE; 601-744 C-NW; 901-1082 C-SW; 1101-3125 C-SE;
3401-4561 F-NW; 4601-5536 F-NW; 5601-6208 F-SW; 6301-6792 F-SE;
6801-7710 K-NE; 7801-8791 K-NW; 8901-9745 K-SW; 9901-10759 K-SE;
10801-11204 S-NE; 11302-14338 S-NW; 14501-17228 S-SW; 18001-18042 S-SE;
18101-18554 U-NE; 18701-19446 U-NW; 19601-20292 U-SW; 20401-21202 U-SE
Range Domain:
Range Domain Minimum: 1
Range Domain Maximum: 21,200
Attribute Units of Measure: increments by 1
Attribute:
Attribute Label: TWPGRID#
Attribute Definition: Internal feature number.
Attribute Definition Source: ESRI
Attribute Domain Values:
Unrepresentable Domain: Sequential unique whole numbers that are automatically generated.
Attribute:
Attribute Label: TWPGRID-ID
Attribute Definition: User-defined feature number.
Attribute Definition Source: ESRI
Overview Description:
Entity and Attribute Overview: Statewide protracted township grid based on BLM's official protraction diagrams.
Entity and Attribute Detail Citation: Attributes are abstracted from BLM's official protraction diagrams.
Distribution Information
Section Index
Distributor:
Contact Information:
Contact Person Primary:
Contact Person: Tom Deiling, Chief, Branch of Spatial Records
Contact Organization: Division of Cadastral Survey and Geomatics, Branch of Spatial Records
Contact Position: Chief Branch of Spatial Records
Contact Address:
Address Type: mailing address
Address: 222 W. 7th Ave. #13
City: Anchorage
State or Province: AK
Postal Code: 99513
Country: USA
Contact Voice Telephone: 9072713797
Contact Facsimile Telephone: 9072714549
Contact Electronic Mail Address: Tom_Deiling@ak.blm.gov
Hours of Service: 0800-1630
Resource Description:
twpgrid.e00 - Available as a gzipped arc/info coverage
twpgrid.shp - Available as a ESRI shape file
Standard Order Process:
Digital Form:
Digital Transfer Information:
Metadata Reference Information
Section Index
Metadata Date: 2/8/2001
Metadata Review Date:
Metadata Future Review Date:
Metadata Contact:
Contact Information:
Contact Person Primary:
Contact Person: Tim Varner
Contact Organization: Bureau of Land Management, Alaska State Office, Division of Cadastral Survey and Geomatics, Branch of Spatial Records
Contact Position: Spatial Database Administrator
Contact Address:
Address Type: mailing address
Address: 222 W. 7th Ave. #13
City: Anchorage
State or Province: AK
Postal Code: 99513
Country: USA
Contact Voice Telephone: 907-271-5799
Contact Facsimile Telephone: 907-271-4549
Contact Electronic Mail Address: Tim_Varner@ak.blm.gov
Hours of Service: 0800-1630
Metadata Standard Name: FGDC Content Standards for Digital Geospatial Metadata
Metadata Standard Version: FGDC-STD-001-1998
Metadata Time Convention: local time
Metadata Extensions:
Online Linkage: http://www.esri.com/metadata/esriprof80.html
Profile Name: ESRI Metadata Profile
SMMS Metadata report generated 2/20/2001