D - Glossary of Engineering Levelling & Surveying

Data

A representation of facts, concepts or instructions in a formalized manner suitable for communication, interpretation or processing.

Data Capture

The encoding of data. In the context of digital mapping, this includes digitizing, direct recording by electronic survey instruments and the encoding of text and attributes by whatever means.

Data Format

A specification that defines the order in which data is stored or a description of the way data is held in a file or record.

Data Point

A coordinate pair which defines the position of a point feature or one of a series of coordinates pairs which define a line feature.

Data Quality

Attributes of a dataset which define its suitability for a particular purpose, e.g. Completeness, positional accuracy, currency, logical structure etc.

Data Type

This defines the structure of a data item. This in turn determines the range of values it can take and the range of operations that can be applied to it. Integer, real and character string are examples of data type. Some modern programming languages allow user-defined types.

Datum

A known position from which all height information is relatively measured. The heights expressed for points mapped on the National Grid are expressed as a height difference in metres from a known point on the harbour wall in Newlyn, Cornwall.

DCDB

The Digital Cadastral Database is the spatial representation of every parcel of land in Queensland. This is along with its legal Lot on Plan description and relevant attributes. It provides the map base for systems dealing with land related information.

Demographic Data

Statistical data on human populations.

Demography

The statistical study of human populations, particularly with reference to size, constitution, density and distribution.

Derived Map

A map which has been produced by reference to other source data, rather than directly from a survey.

Deepwater habitat.

Any open water area in which the mean water depth exceeds 6.6 feet in nontidal areas or at mean low water in freshwater tidal areas, or is covered by water during extreme low water at spring tides in salt and brackish tidal areas, or covers the deepest emerging vegetation.

Developed land.

A combination of land cover/use categories, large urban and built-up areas, Small built-up areas, and rural transportation land.

Descriptive Group

The group to which the primary descriptive attributes of a feature belongs e.g. road/track, building, inland water.

Differential Leveling

Differential levelling is the term applied to any method of measuring directly with a graduated staff the difference in elevation between two or more points.

Digital Audio Tape

A storage medium that is increasingly used for data storage. A DAT cartridge is slightly larger than a credit card and contains magnetic tape that can hold from 700MB to 2.3GB of data.

Digital Elevation Model

A 3D representation of the height and shape topography of the Earth's surface. A DEM is formed by a regular grid of height values and can be overlaid with other data to create DTM.

Digital Map

A term used by Ordnance Survey to describe a particular tile of digital map data.

Direction

Angular measure by reference to a defined line.

Distance

Lineal length between points on a straight line.

Due North

Normally infers True North; use of term is not recommended without a basis of reference.