Monte Mario (EPSG:4265)
Jun 12,2026

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Introduction

Monte Mario (EPSG:4265) is Italy's official two-dimensional geographic coordinate system. Named after the Monte Mario datum and based on the International 1924 ellipsoid, it covers the entire territory of Italy (including San Marino and Vatican City). It is primarily used for geodetic surveying and offshore mineral management. Its coordinate axes are latitude and longitude, measured in degrees. It can be transformed to common coordinate systems such as WGS84 and ETRS89, with an accuracy of approximately 4 meters when transforming to WGS84.

Coordinate System Composition

Overall Coordinate System Type: 2D geographic coordinate system (GEOGRAPHIC_2D_CRS); a geospatial reference system expressing geographic locations via latitude and longitude.
Geodetic Datum: Name: Monte Mario; Ellipsoid: International 1924, with a semi-major axis of 6,378,388 meters and a reciprocal flattening of 297. The unit of length is the meter.
Prime Meridian: Greenwich Meridian; longitude origin is 0, angular unit is degree.
Coordinate Axes: The first axis is latitude, positive north; the second axis is longitude, positive east. The angular unit for both axes is the degree.

Pros

Local Adaptability: As Italy's national datum, its parameters (such as the International 1924 ellipsoid) are well matched to Italy's geographic characteristics. Its long-term use in national surveying has produced a complete body of survey results, ensuring direct compatibility with historical data.
Regional Accuracy Assurance: Based on a rigorous mathematical ellipsoid model, computed lengths and angles deviate only slightly from the actual geoid over Italy, meeting the accuracy requirements of regional surveying.
Coordinate Transformation Support: Through methods like the seven-parameter model, it can achieve relatively accurate transformation (approx. 4 meters) to global systems such as WGS84 and ETRS89, supporting modern surveying and data integration with global frameworks.

Cons

Regional Limitation: Suitable only for Italy and very small surrounding areas; cannot support global or other regional surveying applications. Its general applicability is low.
Accuracy Limitation: Due to the measurement accuracy of the 1924 ellipsoid (the semi-major axis has an error of approx. 109 meters compared to modern ellipsoid parameters), its overall positioning accuracy is lower than that of GNSS-based modern systems (such as ETRS89), making it difficult to meet high-precision modern surveying requirements.
Technological Substitution: As a traditional regional datum, it is gradually being replaced by the more accurate and more universally applicable ETRS89 coordinate system. Relevant update and support are diminishing, and its adaptability to emerging applications is insufficient.

Application Scenario

Monte Mario (EPSG:4265), as Italy's national datum coordinate system, has long served the domestic surveying and mapping sector. It is primarily used for basic geographic information collection, land resource surveys and planning, as well as topographic mapping and construction positioning in engineering surveying within Italy. Additionally, it provides geographic coordinate references for offshore mineral resource exploration and development, and supports the transformation and linking of historical survey data with modern global coordinate systems (e.g., WGS84).