Coordinate system

Jump to the .prj downloads and instructions.

Linked sources open in a new tab.

A journey through old mining plans

An old mining plan also tells a story about the landscape. Finding a mining concession (pertenencia) again meant recognizing the place, its markers, and the traces of human work. Under the Mining Code of 1888, the starting point was a shaft or mine entrance that had to reach at least five meters of vertical depth. From that working, the engineer or surveyor established the concession, placed durable boundary markers, and recorded bearings relative to magnetic north. Where possible, they also recorded the distance and direction to fixed, visible objects nearby. Measurements were already expressed in meters and hectares; their connection to the land depended on these references that others had to be able to recognize. (1888 Code, Articles 35, 37, 52, and 55)

Under the 1932 Code, the reference monument became central: a solid structure at least two meters tall, intended to establish the location of one concession or a group of concessions. The survey's starting point was tied to that monument and could be identified through three sight lines toward distinctive features of the terrain, or through a bearing and distance. The way north was determined also changed: orientation was referenced to the astronomical meridian. Where that meridian had not been determined in the mining locality, the Code allowed the use of a compass, with the magnetic declination recorded—the difference between compass north and geographic north. (1932 Code, Articles 40, 41, and 54)

Coordinates also had a role. The 1932 Code allowed the use of government monuments established through topographic or geodetic surveys, with known coordinates and identification in the survey record. Nearby landscape references thus coexisted with points established by technical surveys. The plan, the survey record, and the preservation of monuments made it possible to reconstruct that sequence of measurements later. Reading these documents offers a glimpse into the craft of those who had to leave a clear and lasting location for the miners and surveyors who followed. (1932 Code, Articles 40, 55, 56, and 65)

The 1983 Code gave greater prominence to a shared reference: UTM north–south orientation and the UTM coordinates of vertices. Monuments remained, now integrated into a common cartographic description that made it easier to compare concessions. The cadastre we consult today carries the traces of that evolution: work from different periods, increasingly precise instruments, and the same concern for making clear where a mining right begins and ends. (1983 Code, Articles 28, 72, 74, and 77)

What datum, UTM, and zone mean

Datum

The reference that relates coordinates to the Earth. It includes a model of the Earth's shape and how that model is positioned. PSAD56, SAD69, and WGS84 are different references: the same numbers do not necessarily identify the same location.

UTM projection

A way to represent the Earth's curved surface on a plane. It expresses position as Easting and Northing, in meters. UTM is not a datum: it can be used with PSAD56, SAD69, WGS84, and other systems.

Zone and hemisphere

They identify the area covered by that projection. For example, “UTM zone 19 South, PSAD56” provides information missing from “UTM” alone. The order of the Northing and Easting values must also be checked.

Why mining rights use PSAD56 and SAD69

PSAD56 is the Provisional South American Datum of 1956, originating at La Canoa, Venezuela, and using the International 1924 ellipsoid. SAD69 is the South American Datum of 1969, tied to Chuá, Brazil, and the South American 1969 ellipsoid. These regional references predate modern satellite positioning and were established through networks of points surveyed on the ground.

Their adoption, together with UTM coordinates, helped organize concession locations and compare their boundaries on a common basis. The word “provisional” in PSAD56 does not remove its legal validity. Its continued use today reflects both the regulations and the continuity of existing plans, mining surveys, and registrations; replacing these datums requires protecting the location of existing rights and their relationships to one another.

Article 16 of the Chilean Mining Code Regulations establishes these rules:

• If an exploration application (pedimento) or exploitation application (manifestación) expressly specifies a datum for its UTM coordinates, that reference is used.
• If none is specified, PSAD56 is assumed, except where the midpoint of the exploration application or the point of interest of the exploitation application lies south of latitude 43°30′ South: in that case, SAD69 applies.
• Subsequent proceedings always use PSAD56 or SAD69 according to that geographic rule, even if the initial application used another datum. The plans and records specified in the article must state the datum and zone.

How they relate to WGS84 and modern systems

WGS84 is a global, geocentric reference, meaning it is tied to the Earth's center of mass. It is associated with GPS and commonly used for navigation coordinates and digital maps. PSAD56 and SAD69 were fitted regionally and have different origins and ellipsoids. A position expressed in WGS84 therefore needs a datum transformation before it can be compared with a historical mining coordinate. (NGA's WGS84 reference)

The difference can reach tens or hundreds of meters, depending on the location and references being compared. No single correction works throughout Chile. Relabeling a file from “PSAD56” to “WGS84” leaves the numbers unchanged and can place it incorrectly; transforming coordinates calculates the corresponding values in the target system. The quality of the result depends on the original data and the method used.

SIRGAS, the Geodetic Reference System for the Americas, establishes a regional reference compatible with the International Terrestrial Reference System, ITRS, and its ITRF realizations. WGS84 and modern reference frames can be closely aligned, but precise work requires knowing the frame realization and coordinate epoch. Sharing a global reference does not make all data interchangeable. (SIRGAS)

The epoch is the date to which a position refers. In Chile, the ground moves because of tectonic activity and earthquakes: the same physical point can have different coordinates at different dates. Coordinates obtained today with GNSS—the satellite navigation systems that include GPS—must be brought to a common reference and epoch before comparison with an earlier survey.

How PMD transforms coordinates: IGM and NIMA

To display concessions on the map in WGS84, PMD uses regional parameters from the Military Geographic Institute (IGM). We preserve the original coordinates of each record and select the transformation according to its datum and location. This choice improves the alignment of concessions with the map and avoids treating the entire country as though it had the same geodetic characteristics.

It is useful to distinguish two types of parameters published by NIMA, the US agency that preceded today's NGA, whose catalogs distinguish general and regional solutions:

• Generic parameters: these are derived from a combined adjustment for several countries that use the same datum. The continental sets for PSAD56 and SAD69 provide a broad approximation, but do not capture the characteristics of Chilean networks in the same detail.
• Parameters specific to Chile: NIMA also published values with national or regional coverage; for PSAD56, there are separate sets for northern Chile and southern Chile. These differ from the generic parameters and from IGM's parameters. Merely stating “NIMA transformation” is therefore insufficient without specifying which set is used.

We choose IGM's parameters for their better accuracy for Chilean networks. For PSAD56, we apply three sets—North, Central, and South—separated by the 26° and 36° south parallels; for SAD69, we use the set for the southernmost sector. This regional approach better fits local differences in historical networks and reduces discrepancies compared with a generic NIMA transformation. NIMA's parameters for Chile are another regional alternative, but should not be confused with the three IGM sectors used by PMD. IGM's parameters and their scope are described in the IDE Chile technical document on SIRGAS and datum transformations.

The article by René Zepeda, “Aspectos técnicos en la transformación de coordenadas a SIRGAS 2000”, explains the differences between classical geodetic networks and modern reference frames, and the importance of considering their accuracy when transforming coordinates. This is also the limitation we must keep in mind: a better regional fit reduces discrepancies, but does not eliminate all distortions in the old network or correct errors in an original mining survey. The number of decimal places in a calculation does not equate to accuracy on the ground.

What to check when using the map or a file

• Identify the full reference: datum, zone, hemisphere, and units; for modern geodetic data, also the frame and epoch.
• Keep the original information: a coordinate from a plan or registration and its transformed version serve different purposes. Converting coordinates to display a concession does not change its legal title.
• Check the purpose of the conversion: an overlay on satellite imagery helps with orientation, but does not replace the formal mining survey (mensura) or, by itself, establish the legal position of a boundary.

PMD lets you consult coordinates in WGS84 and the regional datum. Different values for the same location are normal. If a concession appears offset from an image, first check the references and supporting records for both layers before concluding that the mining right contains an error.

.prj files for PMD shapefiles

PMD shapefiles preserve the original UTM coordinates and are delivered separately by datum and zone. These .prj files describe that reference and include the regional IGM parameters for transforming to WGS84. The EPSG code in the filename identifies the coordinate system; the IGM sector identifies the regional transformation included.

Download all eight .prj files in a ZIP

PSAD56 · North

Sector north of 26° S.

PSAD56 North · UTM 18 South (EPSG 24878)
PSAD56 North · UTM 19 South (EPSG 24879)

ΔX = −302 m; ΔY = +272 m; ΔZ = −360 m.

PSAD56 · Central

Sector between 26° and 36° S.

PSAD56 Central · UTM 18 South (EPSG 24878)
PSAD56 Central · UTM 19 South (EPSG 24879)

ΔX = −328 m; ΔY = +340 m; ΔZ = −329 m.

PSAD56 · South

Sector south of 36° S, for data originally referenced to PSAD56.

PSAD56 South · UTM 18 South (EPSG 24878)
PSAD56 South · UTM 19 South (EPSG 24879)

ΔX = −352 m; ΔY = +403 m; ΔZ = −287 m.

SAD69 · Far south

For data originally referenced to SAD69.

SAD69 · UTM 18 South (EPSG 29188)
SAD69 · UTM 19 South (EPSG 29189)

ΔX = −79 m; ΔY = +13 m; ΔZ = −14 m.

The ΔX, ΔY, and ΔZ translations are expressed in meters and apply in the PSAD56/SAD69 → WGS84 direction. They are geocentric parameters: do not add them directly to UTM Easting and Northing. All eight files are provided as prepared, with their parameters in the TOWGS84 clause.

How to use the .prj file with your download

1. Extract the shapefile and work on a copy. Keep the .shp, .shx, .dbf, .prj, and .cpg files supplied by PMD together.
2. Identify the datum, zone, and sector. For example, for a PSAD56 layer in UTM zone 19 South in the Central sector, choose PSAD56_UTM19S_EPSG24879_IGM_CENTRO.prj. If the download includes concessions from different IGM sectors, separate them into layers by sector: one .prj describes the entire layer.
3. Match the base filename. If your file is named concesiones.shp, the copy of the selected file must be named concesiones.prj and placed in the same folder. Keep a copy of the previous .prj before replacing it.
4. Reload the layer and check its reference. Assigning this file does not change the geometry's coordinate values. To obtain WGS84 coordinates, reproject the data or configure the transformation the software uses to display it on a WGS84 map. Check that it applies the IGM parameters for the sector.

These files are intended for data originally in PSAD56 or SAD69. If you have already reprojected a layer to WGS84, keep its WGS84 reference; assigning one of these .prj files would interpret its coordinates in a different system and place it incorrectly.

In QGISLoad the regional reference and export a layer in WGS84.

1. Load the shapefile with its .prj and check the coordinate reference system under Layer Properties → Source. If there is an older .qpj file, check it too: QGIS gives it priority over the .prj.
2. If the regional definition is not preserved, go to Settings → Custom CRS…, create a CRS with its own name, and paste the full contents of the .prj as WKT. Validate it and assign it to the layer. Check the selected operation under Settings → Options → Transformations; the EPSG number alone does not confirm that the IGM shifts are being used.
3. To create data in WGS84, use Export → Save Features As…, select WGS84 as the target, and save a new layer. Check the transformation used. Changing only the project CRS changes the display, not the coordinates stored in the shapefile.

See the QGIS documentation on coordinate reference systems and transformations, .prj and .qpj files, and exporting layers.

In ArcGIS ProDefine the projection and select the geographic transformation.

1. Check the layer's source coordinate system. Define Projection lets you assign or correct it, but does not convert the coordinates.
2. To convert them, use Project, choose WGS84 as the target, and explicitly select the regional geographic transformation. Importing the .prj alone does not ensure that ArcGIS applies its TOWGS84 clause.
3. If you cannot find a matching transformation, use Create Custom Geographic Transformation: source geographic coordinate system PSAD56 or SAD69, target WGS84, method Geocentric_Translation, and the sector's ΔX, ΔY, and ΔZ values shown above, including their signs. Then select that transformation in Project and save a new layer.

See the official tools Define Projection, Project, and Create Custom Geographic Transformation.

With GDAL, for advanced usersUse the complete file as the source reference in ogr2ogr.

The -s_srs option accepts the definition file, and -t_srs specifies the target. This example applies only to a PSAD56 layer in UTM zone 19 South, Central sector; adapt the filenames to your files:

ogr2ogr -f "ESRI Shapefile" salida_WGS84.shp PSAD56-H19S.shp -s_srs PSAD56_UTM19S_EPSG24879_IGM_CENTRO.prj -t_srs EPSG:4326

Keep the generated WGS84 .prj with the output. The -a_srs option only assigns a reference and does not replace reprojection. See the official ogr2ogr options.

What the GNSS instructions for mining surveys require

SERNAGEOMIN Exempt Resolution No. 2701, dated December 18, 2025, updated the instructions for using GNSS in mining surveys. It took effect on February 2, 2026, replacing Resolution No. 2449 of 2020. This is an approved update: it allows satellite technology to be used while retaining the reference required by the regulations.

Section 3.1.1 provisionally retains NIMA parameters for transforming WGS84 to the datum prescribed by Article 16, until SERNAGEOMIN formally adopts definitive parameters for Chile. It also requires tie points to have native coordinates in the regulatory datum. These requirements apply to the technical mining survey procedure submitted to SERNAGEOMIN; PMD's IGM transformation is used for its map display.

What comes next: REDGEOMIN, USACH, and the ADELA model

The Universidad de Santiago de Chile, through its Centro de Procesamiento y Análisis Geodésico USC, has worked to modernize the reference used in mining. ANID IDeA I+D project ID23I10147 brings together a reference network, transformation tools, and a deformation model to support GNSS work and account for movement of the land. (USACH geodesy projects)

REDGEOMIN and SIRGAS-CON: a continental reference and its use in mining

SIRGAS-CON is the network of continuously operating GNSS stations that realizes SIRGAS in Latin America and the Caribbean. Its analysis centers produce weekly coordinates and multiyear solutions with positions and velocities. It therefore already accounts for the Earth's movement. REDGEOMIN, the Geodetic Network for Mining in Chile, brings together and processes stations to provide a denser reference across Chile, intended for the cadastre and mining surveys. It is tied to the international frame through IGS stations and develops tools to connect that frame with historical mining datums. The difference lies in the scope, processing, and products for mining; both work with coordinates tied to epochs. (SIRGAS-CON; USACH guide, section 4.1)

REDGEOMIN draws on infrastructure installed for different purposes. The guide documents stations from the Centro Sismológico Nacional (CSN), the Ministerio de Bienes Nacionales, and SERNAGEOMIN's Observatorio Volcanológico de los Andes del Sur (OVDAS), which uses GNSS to observe volcanic deformation. It also includes contributions from USACH and EarthScope/UNAVCO. Its table of access to RINEX observations—the files containing receiver measurements—also identifies IGS, Argentina's RAMSAC, and Brazil's IBGE. This does not mean that all stations from those institutions are included or that all their measurements are public: the guide states that OVDAS observations are obtained upon request. (USACH guide, Figure 11 and Table 6, pages 34–35)

VEMOS and ADELA: from average movement to its evolution over time

VEMOS, the SIRGAS velocity model, estimates how far a location moves horizontally, on average, each year. It allows coordinates to be moved from one epoch to another using a velocity and the elapsed time, within the period covered by each model version. Earthquake jumps must be calculated separately. It is therefore necessary to choose the appropriate version and respect its validity period. (VEMOS description and versions, DGFI-TUM)

ADELA—Analysis of DEformation beyond Los Andes—developed by USACH, describes a more detailed trajectory from series of GNSS observations. It accounts for continuous movement, jumps during earthquakes, and subsequent deformation, whose rate can change over time. It models the East, North, and height components, and estimates displacements between stations through interpolation. This distinction is particularly useful in Chile: after a large earthquake, a single average velocity may be insufficient to represent how the ground evolves. (USACH guide, sections 4.5–4.6 and 7.16–7.17)

To use either model, check its version, coverage, applicable period, and reference frame. Changing the epoch and transforming between datums are different operations that must be coordinated. No motion model removes errors in an original mining survey or, by itself, guarantees millimeter accuracy for historical coordinates.

The Guía técnica para uso de SIRGAS y GNSS en la minería de Chile: REDGEOMIN y épocas de referencia, version 1.0 dated July 14, 2025, explains these developments and proposes technical and legal criteria for their implementation. In particular, sections 8.2 through 8.4 suggest approaches to the transition. These are the document's proposals, not new obligations for rights holders. The guide's record in the USACH repository provides access to its versions.