Glossary

Term	Definition
Accuracy	The closeness of the results of observations, computations or estimates to the true values or the values accepted as being true. Accuracy relates to the exactness of the result and is the exactness of the operation by which the result is obtained.
Administrative area	A blanket term used by Ordnance Survey to refer to all public administrative areas, specifically local government management and electoral areas.
American Standard Code for Information Interchange (ASCII)	A 7bit code for encoding a standard character set.
Area	A spatial extent defined by circumscribing lines that form a closed perimeter that does not intersect itself.
Attribute	An attribute is a property of an entity, usually used to refer to a nonspatial qualification of a spatially referenced entity. For example, a name or descriptive code indicating what an entity represents or how it should be portrayed.
Attribute code	An alphanumeric identifier code used in digital map data to describe each feature in terms either of the object surveyed or its representation on the map (or both).
Coordinates	Pairs of numbers, such as an easting and a northing, expressing horizontal distances along original axes. Alternatively, triplets of numbers measuring horizontal and vertical distances.
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.
Eastings	See rectangular coordinates.
Feature	An item of detail within a map that can be a point and/or symbol, text or line.
Field	A specified part of a record containing a unit of data, such as the date of digitising. The unit of data may be a data element or a data item. Every field has a name and a predefined interpretation.
Geographical information system (GIS)	A system for capturing, storing, checking, integrating, analysing and displaying data that is spatially referenced to the Earth. This is normally considered to involve a spatially referenced computer database and appropriate applications software.
Map scale	The ratio between the extent of a feature on the map and its extent on the ground, normally expressed as a representative fraction, such as 1:1250 or 1:10 000.
Name	The proper name or label of an object (real world) or feature (object abstraction). The descriptive name might consist of one or more text strings or be an attribute of the object or object abstraction.
National Grid	A unique referencing system that can be applied to all Ordnance Survey maps of Great Britain (GB) at all scales. It is used by Ordnance Survey on all postwar mapping to provide an unambiguous spatial reference in Great Britain for any place or entity whatever the map scale. The National Grid is defined by the OSGB36 spheroid.
Northings	See rectangular coordinates.
Object (real world)	A recognisable discrete part of the real world.
Origin	The zero point in a system of rectangular coordinates.
Positional accuracy	The degree to which the coordinates define a point’s true position in the world, directly related to the spheroid and/or projection on which the coordinate system is based.
Precision	The exactness with which a value is expressed, whether the value be right or wrong.
Rectangular coordinates	Also known as XY coordinates or as eastings and northings. These are twodimensional coordinates that measure the position of any point relative to an arbitrary origin on a plane surface (for example, a map projection).
Resolution	A measure of the ability to detect quantities. High resolution implies a high degree of discrimination but has no implication as to accuracy. For example, in a collection of data in which the coordinates are rounded to the nearest metre, resolution is 1 metre, but the accuracy may be ± 5 metres or worse.
Spatial data	Data that includes a reference to a two or threedimensional position in space as one of its attributes. It is used as a synonym for geometric data.
Transfer medium	The physical medium on which digital data is transferred from one computer system to another. For example, DVD.