RSO91 (Revised Saberang Ordnance Survey 1991, EPSG:29873)
Nov 5,2025

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Introduction

RSO91 (Revised Saberang Ordnance Survey 1991, EPSG:29873) is the geodetic datum and projected coordinate system for the Malaysian state of Sabah (northern Borneo). This coordinate system has been adapted to suit the local topography and geodetic environment, and is widely used for infrastructure development, land management, cadastral surveys, and environmental monitoring, particularly in Sabah. RSO91 is a revised and updated version of the previously used RSO (Revised Saberang Ordnance Survey) coordinate system, and is intended to provide a more accurate location reference.

Coordinate System Composition

Reference Coordinate System (Geodetic Datum): RSO91 (Everest 1830 Modified ellipsoid used)
Projection Method: Rectified Skew Orthomorphic
Central Coordinates: 4°N, 115°E (Set for Sabah)
Units: Meters (Plane Cartesian Coordinates)
Target Area: Sabah, Malaysia (Entire Northern Borneo)

Pros

Designed specifically for Sabah, it provides high geodetic accuracy within the region.
The use of a modified oblique orthogonal projection minimizes distortion of shape and area throughout the entire target area.
Widely used in land use planning, cadastral management, and public works practices, it provides a highly consistent foundation for government officials and engineers.

Cons

Limited applicability outside of Sabah, making it unsuitable for expansion to other regions.
Limited direct compatibility with global positioning standards (e.g., WGS84), requiring conversion work.
Insufficient standard support for some modern GIS software and international datasets.

Application Scenario

RSO91 (EPSG:29873) is primarily used in Sabah, Malaysia, for land use planning, urban development, and infrastructure development such as roads and public facilities. It is also ideal for tasks requiring geographic accuracy, such as cadastral surveying, forestry management, and environmental monitoring. It plays an especially important role in wide-area land boundary management and resource utilization optimization, and is used in a wide range of applications, from local government to private construction projects. Furthermore, data based on RSO91 can be converted to other international reference coordinate systems (e.g., WGS84 and UTM), enabling international data integration.