Protracted Township Grid for Alaska (NAD83)

Title: Protracted Township Grid for Alaska (NAD83)
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 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 Township table is a spatially-enabled table that contains all of the protraction information for each of the 18,654 townships. Township shapes are stored as NAD83 geographic multipolygons. Each township was individually constructed from NAD83 geographic pro_pt83 (Protracted Point) table and is fully densified by including all township/section offset corners from adjacent township/sections. The geometry for a single township may include as many as 44 coordinates on the exterior ring.
The township table identifies 18,654 townships as 18,654 multi-polygons (four townships require two polygons each), as depicted on the official BLM protraction diagrams.
MTR Number of Geometries ----------------------------------------------------------- C034S048E 2 C040S073E 2 C066S098E 2 C034S067E 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) )

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

Range of values

Minimum:

Maximum:

21,200

Units:

Value	Definition
S	Seward Meridian
C	Copper River Meridian
F	Fairbanks Meridian
U	Umiat Meridian
K	Kateel River Meridian

Value

Definition

Seward Meridian

Copper River Meridian

Fairbanks Meridian

Umiat Meridian

Kateel River Meridian

Value	Definition
N	North of the baseline
S	South of the Baseline

Value

Definition

North of the baseline

South of the Baseline

Value	Definition
0	0 indicates this is not a fractional township
2	2 indicates this is a fractional township

Value

Definition

0 indicates this is not a fractional township

2 indicates this is a fractional township

Value	Definition
E	East from the Principal Meridian
W	West from the Principal Meridian.

Value

Definition

East from the Principal Meridian

West from the Principal Meridian.

Value	Definition
0	0 indicates this is a fractional range
2	2 indicates this is a fractional range

Value

Definition

0 indicates this is a fractional range

2 indicates this is a fractional range

Protracted Township Grid for Alaska (NAD83)

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