Survey, mapping and digital construction terms in plain English.

A coordinated spatial record of terrain, levels and agreed existing natural/constructed features for design, construction or other project use.

A 3D line used to define an important change in terrain geometry, such as a kerb edge, top/bottom of bank or other slope discontinuity.

Triangulated Irregular Network: a terrain/surface representation built from 3D points and breaklines connected as triangles.

Digital Terrain Model: a representation of ground terrain. The exact meaning can vary between software/workflows, so deliverables should be defined rather than relying only on the acronym.

Digital Surface Model: a surface representing visible top surfaces, which can include buildings, vegetation or other objects as well as ground.

A composite aerial image made from overlapping photographs that has been geometrically corrected and georeferenced so it can be used like a map.

A collection of three-dimensional points representing visible or measured surfaces. Point clouds can come from photogrammetry, LiDAR or terrestrial scanning; the acquisition method matters.

The reconstruction and measurement of 3D information from overlapping photographs taken from different viewpoints.

A laser-based ranging technology that directly measures distances. It is a different acquisition method from photogrammetry.

Real-Time Kinematic GNSS positioning using corrections to improve positioning precision during observation.

Stable coordinate and level references used to keep field surveys, setting out, aerial mapping and construction data in one consistent spatial framework.

An exchange format commonly used for terrain surfaces, alignments and other civil engineering geometry between compatible systems.

The spatial difference between a measured/current surface and an agreed reference/design surface, usually separated into material above and below the reference.

Measurement of selected completed work to record actual position, level or geometry, optionally compared against approved design information.

A prepared 3D surface and/or linework dataset used by compatible machine-guidance systems and built from approved project design information.

A project materials-management document used within the relevant regulatory/environmental framework. Survey support can provide spatial and quantitative records such as stockpile volumes, material zones, repeat surveys and quantity reconciliation.

A project-specific coordinate system used instead of or in addition to a national mapping grid. The relationship must be understood before combining datasets.

The Ordnance Survey National Grid reference framework used for mapping in Great Britain. Appropriate transformations and vertical datums must be handled correctly for survey use.