Protracted Section Grid for Alaska (NAD83)

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What does this data set describe?

Title: Protracted Section Grid for Alaska (NAD83)
Abstract:
Section boundaries were generated from geodetic latitude and longitude coordinate pairs as recorded on BLM's official protraction diagrams of the state of Alaska.
The SDMS_PROD protraction tables were modified to include pro_pt83, section83, and township83. The latitude and longitude values in the pro_pt83 table were transformed from geographic NAD27 coordinates to geographic NAD83 coordinates using NADCON for Alaska.
The Informix Section83 table is a spatially-enabled table that contains all of the protraction information for each of the 655,483 sections. Section shapes are stored as NAD83 geographic multipolygons. Each section was individually constructed from NAD83 geographic pro_pt (Protracted Point) table and is fully densified by including all township/section offset corners from adjacent township/sections. The geometry for a single section (i.e. SEC 1, T69S, R100E, CM) may include as many as 11 coordinate pairs on the exterior ring.
The section83 table identifies 655,483 sections as 655,485 multi-polygons (two sections require two polygons each), as depicted on the official BLM protraction diagrams.
MTRS Number of Geometries ----------------------------------------------------------- C033S066E27 2 C066S098E34 2
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.
Township and Section Protraction Re-engineering: A. Added Section Table
B. Add shapes to township and section tables: 1. Spatially-enable township, section, and pro_pt tables to include shape and objectid fields. a. Township shape field ST_Multipolygon b. Section shape field ST_Multipolgon c. Pro_pt shape field ST_Point d. Objectid set to not null, number (38)
C. Add formatted MTR to township and section tables.
C. Add land desc label field to township and section tables.
D. Altered base protraction tables to: 1. Add fields to record the twp and sec pt labels, relative to the twp/sec being defined. Such as: NW, SW, SE, NE, IP, etc. 2. Add field to pro_pt to distinguish protraction points from construction points. 3. Associated the construction points to the appropriate twp/secs based on data in source data file.
E. Updated the township features from ST_Multipolygon shapes consisting of only points at the township corners to ST_Multipolygon shapes also containing points of intersect where section lines meet the township boundary. 1. Densified the township shape features with section corners that fall along the twp lines.
F. Determined all possible section corners for each township using explicit database relationships.
G. Ran program that used Informix Spatial DataBlade and Java 2D framework to densify the boundary by determining the distance between each section corner and all township's boundaries; inserted any points within an extremely small tolerance (0.0000001 degrees) into the township ST_Multipolygon feature. About 1/50,000 were false positives, causing self-intersection errors and manually corrected.
H. Manually edited the only four townships having more than one polygon making up it's shape.
I. Spatially verified topology by comparing shapes of sections dissolved to the township to shapes of the township.
SELECT * FROM township WHERE NOT ST_Equals(shape, (select SE_Dissolve(shape) from section where section.twp_tin_no = township.twp_tin_no) )
  1. How should this data set be cited?

    U.S. Dept. of Interior, Bureau of Land Management, Division of Support Services, Branch of Information Resource Management, 20061208, Protracted Section Grid for Alaska (NAD83).

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -179.230436
    East_Bounding_Coordinate: 179.893985
    North_Bounding_Coordinate: 71.468273
    South_Bounding_Coordinate: 51.201455

  3. What does it look like?

  4. Does the data set describe conditions during a particular time period?

    Calendar_Date: 01-Nov-2006
    Currentness_Reference: publication date

  5. What is the general form of this data set?

    Geospatial_Data_Presentation_Form: vector digital data

  6. How does the data set represent geographic features?

    1. How are geographic features stored in the data set?

      This is a Vector data set. It contains the following vector data types (SDTS terminology):

      • G-polygon (655483)
      • Label point (18658)
      • GT-polygon composed of chains (18685)
      • Point (4)

    2. What coordinate system is used to represent geographic features?

      Horizontal positions are specified in geographic coordinates, that is, latitude and longitude. Latitudes are given to the nearest 0.0000001. Longitudes are given to the nearest 0.0000001. Latitude and longitude values are specified in Decimal degrees.

      The horizontal datum used is North American Datum of 1983.
      The ellipsoid used is Geodetic Reference System 80.
      The semi-major axis of the ellipsoid used is 6378137.000000.
      The flattening of the ellipsoid used is 1/298.257222.

  7. How does the data set describe geographic features?

    sdms_prod:akinfrmx.section83
    PLSS Townships defined by BLM-Alaska Official Protraction Diagrams (Source: BLM-Alaska Official Protraction Diagrams)

    twp_tin_no
    Township TIN Number is an indexing system in Alaska for townships. Each township in the state has a unique 5 digit index number. (Source: Bureau of Land Management)

    Range of values
    Minimum:1
    Maximum:21,200
    Units:1

    objectid
    Internal feature number. (Source: ESRI)

    Sequential unique whole numbers that are automatically generated.

    shape
    Feature geometry. (Source: ESRI)

    Coordinates defining the features.

    user_id
    The system User ID of the person who entered the original data for this record. (Source: Spatial Data Management System, BLM-Alaska)

    ValueDefinition
    twohlwenTom Wohlwend

    entered_date
    The system date that the original data was entered for this record. (Source: Spatial Data Management System, BLM-Alaska)

    ValueDefinition
    2001-02-06February 6, 2001

    modified_user_id
    The system User ID of the person who modified the original data for this record. (Source: Spatial Data Management System, BLM-Alaska)

    ValueDefinition
    j05bondJarad Bond

    modified_date
    The system date that the original data for this record was modified. (Source: Spatial Data Management System, BLM-Alaska)

    ValueDefinition
    2006-05-25May 25, 2006

    SE_Area(shape)
    Automatically calculated area of polygon. (Source: ESRI)

    Area of the feature defined by the coordinates.

    SE_Length(shape)
    Automatically calculated length of polygon line segment. (Source: ESRI)

    Area of the feature defined by the coordinates.

    Length of the line segments of the feature defined by the coordinates.

    tin_sec_no
    Unique identifier for a section in Alaska. Consists of a concatenation of township index number and the two digit, zero-filled section number. Note that while the township index number is a five digit integer, it is not zero filled. (Source: Spatial Data Management System, BLM-Alaska)

    Varies by township/section

    Varies by township/section

    sec_no
    Section Number identifies a protracted "section" within a given township. Sections are generally numbered from 1-36. (Source: Spatial Data Management System, BLM-Alaska)

    Range of values
    Minimum:1
    Maximum:21,200
    Units:1

    Range of values
    Minimum:1
    Maximum:36
    Units:1

    sec_mtrs_txt
    This is a "zero filled" format description of a section. MTRS contains a formatted, concatenated grouping of meridian code, township, township direction, township fraction (if fractional), range, range direction, range fraction (if fractional), section number. (Source: Spatial Data Management System, BLM-Alaska)

    Varies by township/section

    Varies by township/section

    sec_desc_txt
    This is a label field for a section constructed by concatenating tier, range, meridian and section number into a narrative description. (Source: Spatial Data Management System, BLM-Alaska)

    Area of the feature defined by the coordinates.

    Varies by township/section

    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.


Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)

  2. Who also contributed to the data set?

    BLM Official Protraction Diagrams; International Boundary Commission for Alaska/Canadian Boundary; ADNR for ongoing coordination

  3. To whom should users address questions about the data?

    Dennis Walworth
    Division of Support Services, Branch of IRM, Data Management Section
    Data Administrator
    222 W. 7th Ave. #13
    Anchorage, AK 99513
    USA

    (907) 271-3237 (voice)
    (907) 271-4549 (FAX)
    dwalwort@blm.gov

    Hours_of_Service: 0800-1630


Why was the data set created?

For GIS mapping and analytical use. The spatially-enabled township table 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.


How was the data set created?

  1. From what previous works were the data drawn?

  2. How were the data generated, processed, and modified?

    Date: 14-Feb-2001 (process 1 of 4)
    See Abstract and Supplemental Information for process steps.

    Person who carried out this activity:

    Tom Wohlwend
    Bureau of Land Management, Alaska State Office, Division of Cadastral Survey and Geomatics, Branch of Spatial Records
    Geodesist
    222 W. 7th Ave, #13
    Anchorage, AK 99513
    USA

    (907) 271-4224 (voice)
    (907) 271-4549 (FAX)
    Tom_Wohlwend@ak.blm.gov

    Hours_of_Service: 0800-1630
    Date: 01-Nov-2006 (process 2 of 4)
    Populated Township shape from selection set of protraction points for a given township. Most township shapes were correctly populate without additional intervention. Multipolygon townships and townships along the Canadian International boundary required additional automated and some manual intervention to fully incorporate all township/section offsets.

    Person who carried out this activity:

    Dennis Walworth
    Division of Support Services, Branch of IRM, Data Management Section
    IT Specialist
    222 W. 7th Ave. #13
    Anchorage, AK 99513
    USA

    907-271-3237 (voice)
    907-271-4549 (FAX)
    Dennis_Walworth@ak.blm.gov

    Hours_of_Service: 0800-1630
    Date: 01-Nov-2006 (process 3 of 4)
    Township and Section Protraction Re-engineering: A. Added Section Table
    B. Add shapes to township and section tables: 1. Spatially-enable township, section, and pro_pt tables to include shape and objectid fields. a. Township shape field ST_Multipolygon b. Section shape field ST_Multipolgon c. Pro_pt shape field ST_Point d. Objectid set to not null, number (38)
    C. Add formatted MTR to township and section tables.
    C. Add land desc label field to township and section tables.
    D. Altered base protraction tables to: 1. Add fields to record the twp and sec pt labels, relative to the twp/sec being defined. Such as: NW, SW, SE, NE, IP, etc. 2. Add field to pro_pt to distinguish protraction points from construction points. 3. Associated the construction points to the appropriate twp/secs based on data in source data file.
    E. Updated the township features from ST_Multipolygon shapes consisting of only points at the township corners to ST_Multipolygon shapes also containing points of intersect where section lines meet the township boundary. 1. Densified the township shape features with section corners that fall along the twp lines.
    F. Determined all possible section corners for each township using explicit database relationships.
    G. Ran program that used Informix Spatial DataBlade and Java 2D framework to densify the boundary by determining the distance between each section corner and all township's boundaries; inserted any points within an extremely small tolerance (0.0000001 degrees) into the township ST_Multipolygon feature. About 1/50,000 were false positives, causing self-intersection errors and manually corrected.
    H. Manually edited the only four townships having more than one polygon making up it's shape.
    I. Spatially verified topology by comparing shapes of sections dissolved to the township to shapes of the township.
    SELECT * FROM township WHERE NOT ST_Equals(shape, (select SE_Dissolve(shape) from section where section.twp_tin_no = township.twp_tin_no) )

    Person who carried out this activity:

    Jarad Bond
    Division of Support Services, Branch of IRM, Data Management Section
    IT Specialist
    222 W 7th Ave #13
    Anchorage, AK 99513
    USA

    (907) 271-3255 (voice)
    (907) 271-4549 (FAX)
    Jarad_Bond@ak.blm.gov

    Date: 02-Jan-2016 (process 4 of 4)
    We discovered that the datum transformation used to build NAD83 from the original NAD27 source data was not correct due to a limitation in ESRI tools. The areas in St. Lawrence, St. George, and St. Paul Islands were transformed using the correct grid files and the official USGS NADCON method of transformation. Prior to this update, they had been transformed using the general Alaska grid files.

    Person who carried out this activity:

    Jarad Bond
    Division of Support Services, Branch of IRM, Data Management Section
    IT Specialist
    222 W 7th Ave #13
    Anchorage, AK 99513
    USA

    (907) 271-3255 (voice)
    (907) 271-4549 (FAX)
    Jarad_Bond@ak.blm.gov

  3. What similar or related data should the user be aware of?


How reliable are the data; what problems remain in the data set?

  1. How well have the observations been checked?

    Attributes assigned to the spatially-enabled township table are defined in the BLM-Alaska State data dictionary for townships. Attributes for townships are defined from the BLM official protraction diagrams.

  2. How accurate are the geographic locations?

    Section geometries were spatially dissolved and compared to township geometries. No differences in shape geometries were found.
    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.

  3. How accurate are the heights or depths?

    unknown

  4. Where are the gaps in the data? What is missing?

    There is a one-to-one relationship between each township in the spatial database and on the offical protraction diagrams

  5. How consistent are the relationships among the observations, including topology?

    Spatially verified topology by comparing shapes of sections dissolved to the township to shape of the township.
    SELECT * FROM township WHERE NOT ST_Equals(shape, (select SE_Dissolve(shape) from section where section.twp_tin_no = township.twp_tin_no) )


How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?

Access_Constraints:
Discretionary, contains no sensitive information - generally considered releaseable.
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.

  1. Who distributes the data set? (Distributor 1 of 1)

    Tim Varner
    Division of Support Services, Branch of IRM
    IT Specialist
    222 W. 7th Ave #13
    Anchorage, AK 99513
    USA

    (907) 271-5799 (voice)
    tvarner@blm.gov

    Hours_of_Service: 0800-1630
  2. What's the catalog number I need to order this data set?

    Available internally to BLM only.

  3. What legal disclaimers am I supposed to read?

    No warrany is made by the Bureau of Land Management as to the accuracy, reliability, or completeness of these data for individual use or aggregate use with other data.

  4. How can I download or order the data?


Who wrote the metadata?

Dates:
Last modified: 13-Dec-2006
Last Reviewed: 08-Dec-2006
To be reviewed: 08-Dec-2007
Metadata author:
Tim Varner
Bureau of Land Management, Alaska State Office, Division of Cadastral Survey and Geomatics, Branch of Spatial Records
Spatial Database Administrator
222 W. 7th Ave. #13
Anchorage, AK 99513
USA

907-271-5799 (voice)
907-271-4549 (FAX)
Tim_Varner@ak.blm.gov

Hours_of_Service: 0800-1630
Metadata standard:
FGDC Content Standards for Digital Geospatial Metadata (FGDC-STD-001-1998)
Metadata extensions used:


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