D - Glossary of Engineering Levelling & Surveying
A representation of facts, concepts or instructions in a formalized manner suitable for communication, interpretation or processing.
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.
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.
A coordinate pair which defines the position of a point feature or one of a series of coordinates pairs which define a line feature.
Attributes of a dataset which define its suitability for a particular purpose, e.g. Completeness, positional accuracy, currency, logical structure etc.
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.
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.
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.
Statistical data on human populations.
The statistical study of human populations, particularly with reference to size, constitution, density and distribution.
A map which has been produced by reference to other source data, rather than directly from a survey.
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.
A combination of land cover/use categories, large urban and built-up areas, Small built-up areas, and rural transportation land.
The group to which the primary descriptive attributes of a feature belongs e.g. road/track, building, inland water.
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.
A term used by Ordnance Survey to describe a particular tile of digital map data.
Angular measure by reference to a defined line.
Lineal length between points on a straight line.
Normally infers True North; use of term is not recommended without a basis of reference.