NTF (Paris, Nouvelle Triangulation Française–EPSG:4807)
Jul 16,2026

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Introduction

NTF (Paris), corresponding to EPSG:4807, is the classical French geodetic coordinate system known as the Nouvelle Triangulation de la France. It covers metropolitan France and Corsica and was primarily designed to support national cartographic work across France. It uses the Clarke 1880 (IGN) ellipsoid, the Paris meridian as its prime meridian, and grads as its angular unit. Its fundamental origin is the cross mark at the Pantheon in Paris. For planar mapping, it is commonly associated with Lambert zone projections. Today, it has largely been replaced by the RGF93 coordinate system. Relative to WGS84, its approximate origin offsets are Tx = -168 m, Ty = -60 m, Tz = +320 m, making it a common reference system when working with older French surveying and mapping data in GIS.

Coordinate System Composition

Datum: The datum is the core reference framework of the French New Triangulation system. It defines the positional relationship between the ellipsoid and the Earth’s surface and specifies the Paris meridian as the prime meridian.
Reference ellipsoid: The ellipsoid is Clarke 1880 (IGN), with a semi-major axis of 6,378,249.2 meters, an inverse flattening of 293.466021293627, and meter-based linear units.
Prime meridian: The prime meridian is the Paris meridian, with a longitude of 2.5969213 grads (equivalent to 2.337229 degrees), giving it a fixed offset from the Greenwich meridian.
Angular unit: The system uses grads (gon/grad) as the angular unit, where 1 grad = 0.0157079632679489 radians, rather than the more internationally common sexagesimal degree system.

Pros

Strong regional suitability: NTF (Paris) is built on the Clarke 1880 (IGN) ellipsoid, whose parameters were optimized for the geographic characteristics of mainland France. This allows it to describe the Earth’s surface within France more accurately and reduce measurement error caused by mismatch between the ellipsoid and the actual terrain.
Excellent compatibility with historical data: As the core datum of traditional French triangulation, NTF (Paris) served as the standard reference for early French surveying and mapping data. Because it uses the Paris meridian as the prime meridian, it aligns closely with historical French cartographic practice and helps preserve consistency across old maps, engineering records, and legacy datasets.
Distinctive coordinate representation: It uses grads rather than degrees, dividing a full circle into 400 parts. This has historical continuity within French surveying practice and helps maintain compatibility with older coordinate systems while reducing conversion overhead in legacy workflows.

Cons

Limited global applicability: NTF (Paris) is a local geodetic datum centered on France. Its origin and ellipsoid fit are only well suited to that region. Outside France, or in global-scale applications, the mismatch between the datum and the Earth’s actual geometry increases, resulting in significantly higher error.
Poor compatibility with modern geocentric systems: With the widespread adoption of GPS and other satellite navigation systems, geocentric coordinate systems such as WGS84 have become the standard. Since NTF (Paris) is not geocentric, transformations to WGS84 require more complex mathematical models, such as seven-parameter transformations, and the conversion accuracy depends on the chosen parameters.
Higher cost for international data integration: Because national local datums differ in ellipsoid parameters, orientation, and origin, converting NTF (Paris) to foreign systems such as NAD83 or ETRS89 requires extra steps, including datum transformation and unit conversion between grads and degrees. This reduces efficiency in multinational surveying or cross-regional projects.
Separation of height and horizontal coordinates: NTF (Paris) follows a traditional surveying model in which horizontal coordinates and elevation are handled separately rather than within a unified 3D coordinate framework. In modern 3D positioning scenarios such as autonomous driving or BIM, this adds integration complexity and can introduce synchronization-related positioning error.

Application Scenario

NTF (Paris) (EPSG:4807) is mainly used in France for integrating historical surveying and mapping datasets, topographic map production, and engineering surveying. Because its parameter design is based on the Clarke 1880 ellipsoid and the Paris meridian, it remains well suited to the geographic characteristics of France and is still used as a reference framework in regional land planning, building positioning, and GIS workflows involving legacy data. To ensure compatibility with modern geocentric coordinate systems such as WGS84, coordinate transformation is generally carried out using TOWGS84 parameters to support cross-regional data exchange.