National Land Surveying and Mapping Center. Republic of China(Taiwan)National Land Surveying and Mapping Center. Republic of China(Taiwan)

Four coordinate systems in Taiwan：

Cadastral Coordinate System

• The cadastral coordinate system was established during Japanese Occupation Period by Japanese Governor for taxation of Taiwan lands. This system was a planar rectangular coordinate system, and its origin is of the main triangulation point No. 89 located in Chung-shan Park in Taichung City. The cadastral coordinate was expanded to the entire province for water conservancy, agriculture, and forestry surveys as well. The coordinate measurement results of cadastral points are based on the unit of “Jian”, where 1 Jian = 1/0.55m, and 1 m = 0.55 Jian.

Geodetic Survey System

• This system is of the use for military mapping. With the first order astronomical point of Huzhi Mountain in Puli of Nantou County as the origin which was positioned by the method of astronomical observation. The control points scattered around the whole Taiwan were set with the hierarchical orders of the first, second, third, and fourth. The individual order survey can be conducted in accordance with geodetic astronomical observation and triangular measurement method while calculating the geodetic position (latitude and longitude and azimuth) of each point. The Ministry of the Interior announced the “Table of Taiwan Province Triangular Points Results” in 1970 based on the measurement criteria as shown below:
  • The 1924 international spheroid(Hayford spheroid) is adopted as the reference ellipsoid with the parameters of:
    Semi-major axis (Equatorial radius)：a = 6378388 m
    Semi-minor axis(Polar radius)：b = 6365911.94613 m
    Flattening：f = 1/297
  • Geodetic datum starts from the first order triangular point of Huzhi Mountain in Puli of Nantou:
    LONGITUDE：λ = 120°58’25.975" E
    LATITUDE：φ = 23°58’32.340" N
    The azimuth at the southern end of the Puli baseline α = 243°47’21.611"
    Map projection: 6-degree Universal Transverse Mercator Projection System.

TWD67 Coordinate System

• In light of the severity of damage and missing percentage of control points, the Ministry of the Interior arranged control points inspection and adjustment calculation operation starting from the year of 1976 for enhancement of precision. The “Table of Taiwan Province Triangular Points Results” was then announced in 1980 based on the measurement criteria as shown below:
  • The 1967 international spheroid is adopted as the reference ellipsoid with the value of:
    Semi-major axis (Equatorial radius)：a = 6378160 m
    Semi-minor axis (Polar radius)：b = 6356774.7192 m
    Flattening：f = 1/298.25
  • Geodetic datum starts from the first order triangular point of Huzhi Mountain in Puli of Nantou:
    LONGITUDE：λ = 120°58’25.975" E
    LATITUDE：φ = 23°58’32.340" N
    The azimuth with respect to Touju Mountainα = 323°57’23.135"
  • Map projection: 2-degree Transverse Mercator.

TWD97 Coordinate System

• In light the severe missing and damage to the control points announced in 1980, a total of 8 satellite tracking station, 105 first order satellite points, and 621 second order satellite points were established by GPS surveying technology from 1993 to 1997. This system is named 1997 Taiwan Datum (simply known as TWD97) based on the measurement criteria as shown below:
  • The ITRF is adopted with the azimuth BIH(Bureau International de I’Heure) defined as the azimuth at the time of 1984. 0.
    The reference ellipsoid announced by IUGG in 1980(GRS80) is adopted as the reference ellipsoid with parameters as shown below:
    Semi-major axis (Equatorial radius)：a = 6378137 m
    Flattening： f =1/298.257222101
  • Map projection: 2-degree Transverse Mercator.
• After the 921 Earthquake in 1999, most triangular points in central Taiwan were shifted and could not be used. Therefore, on May 2, 2001 the Ministry of the Interior announced that the surveying datum in the Article 4 of the Cadastral Surveying Implementation Rules should be based on TWD97 system.
• The 2010 results of 1997 Taiwan Datum System (TWD97[2010]): under the effect the tectonic movement, the basic control points in certain areas were significantly shifted such that the surveying results cannot be in compliance with the precision requirements of current mapping operation. Starting from October 2009, the Ministry of the Interior began convening special project meeting and confirmed the adoption of 1997 Taiwan Datum System (TWD97) as the standard framework continually. In the meantime, the 2010 surveying results of 1997 Taiwan Datum System (TWD97 [2010]) was announced on March 30, 2012. The surveying datum and definition of these results are identical to TWD97, yet they are fitted to the 2010.0 time results of international fixed stations.
• On February 6, 2017, an earthquake with a magnitude of 6.26 occurred in the Hualien area of ​​eastern Taiwan. The maximum magnitude of the earthquake in Hualien City reached 7, causing the maximum surface displacement of about 45 centimeters. The interrelationship of the basic control points in the Hualien area was affected. To comply with the basic control point accuracy stipulated in the Land Surveying and Mapping Act, the NLSC coordinated with  the Hualien County Government and the Hualien Land Administration Office to jointly conduct a re-survey of basic control points in the area to maintain Taiwan's geodetic datum.
• The 2020 results of 1997 Taiwan Datum System (TWD97[2020]): Due to tectonic movement, the basic control points in certain areas shifted significantly, such that the surveying results could not comply with the precision requirements of current mapping operations. Starting in April 2020, the Ministry of the Interior began convening special project meetings and confirmed the adoption of the 1997 Taiwan Datum System (TWD97) as the standard framework. Meanwhile, the 2020 surveying results of 1997 Taiwan Datum System (TWD97 [2020]) were announced on August 10, 2020. The surveying datum and definition of these results are identical to TWD97, yet they are fixed to the 2020.0 epoch of international CORS results.
• On September 18, 2022, an earthquake with a magnitude of 6.8 occurred in the Taitung area of ​​eastern Taiwan, causing a maximum surface displacement of about 87 centimeters. The interrelationship of the basic control points from the Ruisui Township, Hualien County, to Taitung City, Taitung County was affected. To comply with the basic control point accuracy stipulated in the Land Surveying and Mapping Act, the NLSC conducted a re-survey of basic control points in the area to maintain Taiwan's geodetic datum.
• The NLSC conducted control point surveying on Tungsha Island from October 28,2022 to November 2,2022, providing results for surveying and mapping operations.
• The NLSC conducted control point surveying on Penghu, Kinmen, Matsu, Lanyu and Green island from March 2023 to June 2023, providing results for surveying and mapping operations.