Voirol 1875 (EPSG:4304)
Sep 24,2026

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Introduction

Voirol 1875 (EPSG:4304) is a historical 2D geographic coordinate system used in the maritime and land areas of northern Algeria above 32°N latitude. It was established by the French IGN Paris and uses the Clarke 1880 (IGN) reference ellipsoid and the Greenwich prime meridian. Units are in degrees, with coordinate axes ordered as latitude (northward) and longitude (eastward). It differs from the Voirol 1879 geodetic datum by approximately 9 meters, and the two were sometimes used interchangeably in the early oil industry. It has now been fully replaced by the Nord Sahara 1959 coordinate system and can be transformed to WGS84 (EPSG:4326) using the transformation methods defined in EPSG.

Coordinate System Composition

Datum definition: The geodetic datum is Voirol 1875, based on fundamental surveying data provided by the French IGN Paris. It is a historical local (non-geocentric) geodetic datum dedicated to northern Algeria.
Reference ellipsoid: Uses the Clarke 1880 (IGN) ellipsoid, with a semi-major axis of 6,378,249.2 m and an inverse flattening of 293.4660212936269.
Prime meridian: Uses Greenwich as the 0° meridian, complying with the general definition rules for meridians in geographic coordinates.
Coordinate system type: Classified as a 2D ellipsoidal geographic coordinate system, with coordinate axis order of geodetic latitude then geodetic longitude, pointing northward and eastward respectively.
Unit of measurement: Uses degrees as the angular unit for latitude and longitude, with EPSG unit code 9102.
Datum transformation parameters: Transformation to WGS84 incorporates geocentric translation parameters (-73, -247, 227), with no rotation or scale components.

Pros

High regional applicability: Uses the Clarke 1880 (IGN) reference ellipsoid with local positioning and orientation in northern Algeria, achieving relatively high consistency between the ellipsoid surface and the local geoid in areas north of 32°N, meeting the needs of early French colonial-era large-scale topographic surveying.
Rich historical data accumulation: As a historical datum established in the late 19th century, it preserves a large volume of observation results from early astronomical and geodetic networks in northern Algeria, serving as an important bridge connecting the country's modern surveying materials with contemporary coordinate systems.
Complete parameter system: The datum definition includes complete parameters such as the ellipsoid semi-major axis, flattening, and prime meridian (Greenwich). Coordinate units use angles (degrees), making it suitable for traditional geodetic calculations and manual coordinate transfer.
Publicly available transformation parameters: The EPSG database clearly provides the 7 parameters used for transformation to WGS84 (geocentric translations: -73 m, -247 m, +227 m), facilitating the migration of historical data to modern coordinate references.

Cons

Low accuracy level: The published accuracy metric for transformation to WGS84 is only about 999 m, representing a large systematic error compared to modern geocentric coordinate systems. It is therefore unsuitable for high-precision positioning or engineering surveying.
High risk of datum confusion: There is a discrepancy of approximately 9 m with the contemporaneous Voirol 1879 geodetic datum, and complete historical documentation regarding the boundary of applicability (32°N latitude) is lacking. In industries such as oil, the two were used interchangeably for a long period.
Incompatible with modern GNSS: As a local (non-geocentric) geodetic coordinate system whose origin is not located at the Earth's center of mass, it cannot be directly matched with the geocentric coordinates output by GPS/GNSS satellite positioning systems. Parameter transformation is required for use.
Limited coverage and already deprecated: It covers only a limited area of northern Algeria, while southern regions required a different historical datum. It has now been fully replaced by more unified datums such as Nord Sahara 1959 (EPSG:3049), and continued use results in a loss of consistency with the current national surveying system.
Outdated ellipsoid parameters: The Clarke 1880 ellipsoid parameters are older than modern ellipsoids such as GRS80 recommended by the International Union of Geodesy and Geophysics (IUGG) in 1975, and lag significantly behind in terms of global consistency and scientific accuracy.

Application Scenario

Voirol 1875 (EPSG:4304) was primarily used for historical map production in areas of northern Algeria above 32°N latitude and for the management of colonial-era geodetic surveying materials. It was also widely used in the oil exploration industry for well location identification and geological material production during early oilfield development. Furthermore, this coordinate system carries a large volume of topographic surveying, cadastral registration, and military mapping data left by French colonial surveying agencies from the late 19th to the mid-20th century. As such, it is a datum that requires focused handling in archaeology, historical geography research, and the digitization and migration of legacy materials. In modern practice, it is mainly used in historical geographic information system (GIS) data conversion and integration scenarios, and connecting it with modern surveying results requires transformation to WGS84 or Nord Sahara 1959 using the 7 parameters defined in EPSG.