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Lisbon 1890 (EPSG:4803) is a regional non-geocentric datum established by Portugal at the end of the 19th century. It primarily provided a unified coordinate framework for the country's early terrestrial surveying and topographic mapping (for example, when combined with the Bonne projection to form EPSG:2963). As a national standard from a specific historical period, it has been completely superseded by modern geocentric datums (e.g., ETRS89). Its current value is limited solely to processing and converting legacy Portuguese data such as historical maps and cadastral archives from the late 19th to mid-20th century, which, after professional conversion, can be used for digital archiving and historical geographic analysis.

Roma40 (Rome 1940, EPSG:4806) is a regional, historical geodetic datum designed specifically for Italy and its surrounding regions (such as Sicily and Sardinia), and belongs to the geocentric coordinate system. Its core purpose was to provide a benchmark for official Italian surveying from the 1940s to the 1990s.

ED87 (European Datum 1987, EPSG:4231) is a regional geodetic datum established in 1987 specifically for Europe, primarily Western Europe. It is a traditional geodetic datum designed to align the coordinate framework as closely as possible with the European geoid at the time and served as a key intermediate achievement in the modernization of European geodesy. Its primary application is in processing historical surveying data, topographic maps, and engineering drawings from Western Europe predating the 1990s. However, as a transitional datum based on terrestrial triangulation, its accuracy and global compatibility are now insufficient. Today, it is mainly used for scenarios such as historical data integration, digital archiving, and specialized research after being transformed into modern geocentric coordinate systems like WGS84 or ETRS89.

NAD27 (North American Datum 1927) is a geodetic datum established in 1927 for North America, defined based on the Clarke 1866 ellipsoid with its origin at Meades Ranch in Kansas, USA. This datum served as the official mapping and surveying standard for the United States, Canada, and Mexico for decades, widely used in historical topographic maps, land ownership records, and traditional geographic data. Although its accuracy is limited by early surveying technology and it has been superseded by more modern datums (e.g., NAD83), a significant number of historical archives and legacy systems still rely on NAD27. Therefore, special attention must be paid to datum transformations when dealing with older geographic data in North America.

Eckert IV (Eckert's Fourth Projection) is an equal-area map projection proposed in 1906 by German mathematician Max Eckert. Designed for representing the entire Earth on a world map, it accurately preserves area while distributing shape distortions relatively evenly. It is commonly used in GIS and thematic mapping for visually representing statistical data and distribution information. It is implemented by ESRI as ESRI:54012.

Mercator projection is a conformal tangent cylindrical projection devised by the Flemish cartographer Gerardus Mercator in 1569. It conceptually projects the Earth's surface onto a cylinder tangent at the equator, with a light source at the Earth's center casting surface features onto the cylinder. When unrolled, this creates a world map with the standard parallel at zero degrees (the equator).

MGRS coordinate system, also known as the Military Grid Reference System, is a standard coordinate system used by NATO military organizations. It is based on the Universal Transverse Mercator (UTM) system and further divides each UTM area into small squares of 100km x 100km. These blocks are identified by two connected letters, with the first letter representing the east-west position of the longitude zone and the second letter representing the north-south position.

Swiss LV95 is a projection coordinate system adopted by the Swiss government, based on the CH1903+/LV95 standard, and is a variant of the Gauss Kruger projection designed specifically for planar surveying in the Swiss region. It solves the problem of direct use of spherical data in engineering and mapping by converting geographic coordinates (such as WGS84) into planar coordinates. This coordinate system is widely used in navigation, land management, and infrastructure planning in Switzerland, and its coordinate values are usually expressed in meters.

Irish Transverse Mercator (ITM) is a transverse Mercator projection coordinate system designed specifically for Ireland, using the ETRS89 ellipsoid as the reference. The central meridian of its projection is 8 degrees west longitude, and the geographic coordinates of the Irish region are converted into plane coordinates through the horizontal axis isometric cylindrical projection method to reduce deformation and meet national surveying and mapping needs. This coordinate system is the primary projection system for official maps and geospatial data of Ireland.

New Zealand Map Grid (NZMG) coordinate system is a projected coordinate system used in New Zealand. Based on the Transverse Mercator projection, it is primarily used for mapping and georeferencing within New Zealand. It projects the Earth's surface onto a flat surface, centered on the South and North Islands of New Zealand. It uses specific central meridians and scale parameters to minimize projection distortion. This coordinate system is widely used in surveying, engineering, and land management in New Zealand. Coordinates are typically expressed in meters, with an origin near the South Island.