Bench Mark - a height datum, usually a cut in stone work, expressed in metres above Mean Sea Level by the Ordnance Survey (OS). A Temporary Bench Mark (TBM) having an arbitrary or OS value may be used in a small project.

Computer Aided Design (CAD) - a generic term now associated with any survey produced in digital format for subsequent design or mapping.

Control - the means by which a project is related to specific fixed points in plan and height, basically to ensure that proposed projects are orientated in relation to existing local features. Modern use is made of satellite positioning for control.

Digital Terrain Modelling (DTM) - The representation of measured, survey data of ground surfaces by a model in 3D. Design may be viewed, rotated and tested against criteria parameters and amended accordingly. Volumes can be calculated arithmetically by the computer very quickly.

Drawing Exchange File (DXF) - a software generated format that allows one set of digital data to be transferred to a different software program. Some modifications may have to be made to ensure universal compatibility.

Drawing File (DWG) - An AutoCad generated format enabling digital data to be transferred in a compressed format to another AutoCad user.

EDM - "Electromagnetic Distance Measurement" - a method of measuring distances using an infrared light to a remote prism surface normally integral with an angle measuring device.

Survey Stations - a marker established to control a survey, to be given co-ordinates - usually a peg, pin in concrete, road nail or ground anchor.

Total Station - an instrument capable of measuring and recording, by electronic means, bearing, distance and height to another point - see also EDM.