What is Ordnance Datum in the UK?

Ordnance Datum (OD) is the standard height reference for the UK, based on mean sea level at Newlyn. Most UK construction and mapping projects use OD as their vertical reference.

For more details about datum points, read our in-depth blog.

Related Questions

How do surveyors choose a datum point on a construction site?

Surveyors select a stable, accessible location and tie it to the project’s chosen datum system using GNSS or total station measurements.

What is the difference between a vertical datum and a horizontal datum?

A vertical datum sets the reference for height or elevation. A horizontal datum sets the reference for position.

Why are datum points important for drone surveys and mapping?

Datum points ensure drone data aligns with ground surveys, design models and existing site coordinates. Without them, maps and measurements can be offset or inaccurate.