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Ordnance Survey - Glossary: mapping terminology and acronyms Category: Electronics and Engineering > mapping Date & country: 24/09/2007, UK Words: 414

Absolute Accuracy
A measure which indicates how closely the coordinates of a point in Ordnance Survey map data agree with the true National Grid coordinates of the same point on the ground. As the true position can never be known exactly, the statistic is quoted relative to the best known position determined by precise survey methods.

Absolute Coordinates
A coordinate pair or triplate measured directly from the origin of the coordinate system in which it lies and not to any other point in the system.

Abstraction
The process of selection, generalisation and aggregation.

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 operation by which the result is obtained.

ActiveX
The name given by Microsoft to a group of technologies which use Microsoft's component model.

Address
A means of referencing an object (feature) for the purposes of unique identification and location.

Address Matching
A geocoding process which matches the street address of property to its location. This usually involves the matching of two database files, one containing the addresses of interest, the other a list of addresses and their coordinates. Address matching is central to many applications in direct marketing.

Addressed Premise
A permanent or non-permanent building structure with an address being a potential delivery point for Royal Mail®.

Administrative Area
A blanket term used by Ordnance Survey to refer to all public administrative areas, specifically local government management and electoral areas.

Aerial Photograph
A photograph taken by a camera mounted onto some form of flying object within the Earth's Atmosphere. The resultant images are used in GIS as a background layer or used by surveyors to digitise.

Aggregation
The grouping together of a selected='selected' set of like entities to form one entity. For example, grouping sets of adjacent area units to form larger units, often as part of a spatial unit hierarchy such as wards grouped into districts. Any attribute data is also grouped or is summarised to give statistics for the new spatial unit.

Agreement Term
The duration of an agreement as defined in the terms and conditions of that agreement.

Aliasing
Visibly jagged steps along angled lines or object edges, due to sharp tonal contrasts between pixels.

Alphanumeric
Information using both letters and numbers.

Analogue
Continuously variable signals or data.

Analysis
A service to derive and supply the answer to a specific question by interrogation and analysis of one or more datasets. The result of the query will be delivered to the customer, but not necessarily in a map-based form.

Annotation
The abiltity to link notes to imaged documents, while leaving the original image unaltered. The user is alerted to the presence of an annotation, usually by an icon on the image.

Arc
A locus of points that forms a curve that is defined by a mathematical function.

Area
A bounded contiguous two dimensional object which may or may not include its boundary. Usually defined in terms of an external polygon or in terms of a set of grid cells.

Area Seed
See Representative Point.

ASP
See Application Service Provider.

Associated Data
Datasets held by third parties that have been linked to features within OS MasterMap by means of identifiers (TOID) or coordinate positioning.

Attribute
Descriptive information about features or elements of a database. For a feature like census tract, attributes might include many demographic facts including total population, average income and age. In statistical parlance, an attribute is a 'variable', whereas the database feature represents an 'observation' of the variable.

Attribute Accuracy
Component of data quality describing the likelihood of an attribute of a spatial feature being erroneous.

B2B
Business to business. In an e-business context, using internet technology to enable interaction between businesses.

B2C
Business to consumers. In an e-business context, using internet technology to enable interaction between a business and its consumers.

Backdrop Map
A 'dumb' map or image whose primary use is to provide context visually. It contains no other intelligence or attribution other than what is needed to provide the background. There is currently no OS MasterMap backdrop map product.

Base Mapping
Usually associated with topographic mapping covering country or region at different scales.

Basic Land and Property Unit
The physical extent of a contiguous area of land under uniform property rights.

Basic Scale
The scale at which the survey is undertaken. For Ordnance Survey mapping, three scales (1:1250 - urban, 1:2500 - urban and rural, 1:10 000 - mountain and moorland) are used.

Baud
Bits per second. A measurement used in data transfers via telephone lines.

Bearing
Bearings are angles measured against the National Grid in degrees. They are measured clockwise from grid north.

Bench Mark
A survey point on a fixed object, the altitude of which has been surveyed in relation to Ordnance Datum or the applicable local datum, which in turn is related to mean sea level.

Bitmap
A digitised image that is mapped into a grid of pixels. The colour of each pixel is defined by a specific number of bits.

BLPU
See Basic Land and Property Unit.

Boundary
The limit of a pre-defined and established area whose limit is determined by one or more lines e.g. County area boundary, reservoir boundary.

Browser
An application which gives the user the ability to view a graphic representation of mapping data. The application would provide tools (e.g. pan, zoom) to aid this viewing. It provides a visual representation of the mapping data, which may displayed at a variety of resolutions dependent on the size of area being displayed.

Buffer
A zone of user-specified distance around a point, line or area. The generation of buffers to establish the proximity of features is one of the most common forms of GIS analysis. For example, it may be used to find all areas of industry less than 5km from a reservoir.

Building
A physical walled structure, connected to foundations, which has or will have a roof i.e. this definition includes buildings surveyed at the foundation stage.

CAD
See Computer Aided Design.

Cadastral Survey
A survey of the boundaries of land parcels.

Cadastre
A public register of land recording the extent and value of land parcels for the purposes A dataset containing information related to land ownership and rights. This usually takes the form of maps and descriptions of uniquely identifiable land parcels. For each parcel, legal information such as ownership, easements and mortgages are recorded More information can be found on the HMLR web site.

Calibration
The act or process of comparing certain specific measurements in an instrument with a standard.

Cartesian Coordinates
Numbers expressing the location of a point in two or three dimensions as the perpendicular distances from two or three orthogonal axes.

Cartography
The organisation and communication of geographically related information in either graphic or digital form. It can include all stages from data acquisition to presentation and use.

Census
A survey of the public. Usually organised by national governments to determine the characteristics of the population. For example the UK has a decennial census (every ten years), the next one scheduled for 2001.

Change-only update
The ability to supply to a customer only those features within OS MasterMap which have been created or changed since a specified date. Change-only supply includes a list of the TOIDS of deleted features. In the OS MasterMap context, the selection of changed data will be by 'change since date' (i.e. all change since the specified date). It is not possible to select 'change since my last update'. Therefore the customer system must recognise repeatedly supplied features.

Character
A distinctive mark: an inscribed letter: one of a set of writing-symbols.

Character Set
A set of letters, numerals, punctuation marks, mathematical and other symbols. Standard sets have been drawn up by ANSI, ISO and others.

Character String
A one-dimensional array of characters held either in memory or in another storage medium.

Choropleth Map
A class of thematic map portraying area properties using shaded symbols. Common choropleth maps are population maps.

Classification
An attribute value assigned to a feature that provides a categorisation of the feature normally in terms of type or use: e.g. A polygon feature could be classified as a building or hospital. Dependent on the limitations of product or database system a feature may have multiple classifications.

Client-Server
A network arrangement with one or more powerful computers at the centre and a string of less powerful workstations at the periphery.

Clipping
The conversion of all tones lighter than a specified grey level to white, or darker than a specified grey level to black, causing loss of detail. This also applies to individual channels in a colour image.

COGO
See Coordinate Geometry.

Coincident Line Feature
A feature derived from the merging of vectors from the same or different features, having coincident or near coincident alignments (as determined by a set tolerance) and feature code. Coincident features carrying certain feature codes constituting fdifferent thematic layers are not merged e.g. boundaries and landform.

Collective Agreement
An agreement where two or more organisations (i.e. separate legal entities) jointly request a Period Licence Service.

Completeness
Component of data quality describing the completeness of coverage within a dataset or datasets.

Computer Aided Design
Software programs for the design, drafting and presentation of graphics. Originally designed for manufacturing drawing, now widely used for mapping.

Configuration
Term used for the arrangement of hardware and software. The way in which a computer is set up in a standalone or networked environment.

Conflation
The process whereby two maps of the same area, usually from different time periods or different themes, can be matched and merged together.

Contiguous
Literally adjacent, touching. In the context of digital mapping, the word has a special meaning and implies a connected entity.

Contour
A line drawn on a map joining locations of equal height. Many of these at different heights indicate the shape of the landscape. This is a type of isoline.

Control
A system of points which are used as fixed references for positioning other surveyed features.

Conventional Archive
Map information stored in non-digital form e.g. On paper. The conventional archive exists in a very wide range of formats which reflect differences in the methods used to gather the information, differences in the product items which are produced from the archival information and also differences in production techniques which have been adopted over the years.

Cookies
These are designed to store information about the User to personalise their Internet/Intranet experience. They are useful for holding information on repetitive tasks and applications that an individual user might have.

Coordinate Geometry
Algorithms for handling basic two and three dimensional vector entities built into all surveying, mapping and GIS software.

Coordinate Pair
An X and Y value measured with reference to Cartesian axes. In mapping, a coordinate pair normally consists of an easting and a northing.

Coordinate Point
See Coordinate Pair.

Coordinate Transformation
The computational process of converting an image or map from one co-ordinate system to another. Is also known as a transformation.

Coordinate Tuple
see Tuple.

Coordinates
Pairs of numbers expressing horizontal distances along orthogonal axes, or triplets of numbers measuring horizontal and vertical distances.

Copyright
Copyright is a legal property right which enables the creator of an original work to protect it from unauthorised use. Through the Copyright, Designs and Patents Act 1988, Crown Copyright continues to subsist in all Ordnance Survey products until the end of the period of 50 years from the end of the year in which they were published. In the case of digital data this is from the end of the year in which they are extracted from the Ordnance Survey database. Crown Copyright is vested in the Controller of Her Majesty's Stationery Office, who has delegated powers to the Director General, Ordnance Survey for the administration of copyright in Ordnance Survey publications and data, including the determination of rules and terms under which permission for their reproduction is given.

COU
See Change-only update.

Coverage
A special type of feature which returns a value (e.g. a height or a temperature) for any given point in the domain over which the coverage is defined. A coverage could be implemented as a grid (e.g. a digital terrain model), an image, a triangulated irregular network (TIN) or a mathematical function which calculates a value at the requested coordinates.

DAT
See Digital Audio Tape.

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

Data Capture
The encoding of data. In the context of digital mapping, this includes digitising, 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 Mining
The non-trivial process of identifying valid, novel potentially useful and ultimately understandable patterns in data. Uses techniques such as neural nets, genetic algorithms and machine induction.

Data Model
A generalised, user-defined view of data representing the real world.

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

Data Protection Registrar
An independent officer reporting directly to Parliament who is reponsible for administering the Data Protection Act 1984.

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

Data Streaming
See Feature Serving.

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.

Databank
A collection of data in a common location relating to a given set of subjects.

Database
Physical management system for one or more datasets.

Database Right
Database Right is a legal property right as defined in the Copyright and Rights in Databases Regulations 1997 implementing Council Directive No. 96/9/EC of 11 March 1996 on the legal protection of databases. Database Right enables the maker of a database to protect it from unauthorised use. Crown Database Right subsists in all Ordnance Survey databases until the end of 15 years from the end of the calendar year in which the database was first made available to the public. Any substantial change to the contents of a database will qualify the database for a new term of protection. Crown Database Right is vested in the Controller of Her Majesty's Stationery Office, who has delegated powers to the Director General, Ordnance Survey for the administration of Database Right in Ordnance Survey publications and data, including the determination of rules and terms under which permission for their use is given.

Dataset
A set of data that share common characteristics and that are managed as a subset of the data within a database. For example TOPO, ROADS and ADDRESS are OS GB datasets from which the products Land-Line, OSCAR and ADDRESS-POINT are respectively derived.

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 meters from a known point on the harbour wall in Newlyn, Cornwall.

DCOM
Distributed Component Object Model.

DCW
See Digital Chart of the World.

Decompression
The expansion of compressed image files.

Delivery Point
A Royal Mail defined point to which mail is delivered. This may be a property, organisation, mailbox or even the name of an individual. These categories are derived from 'The complete guide to postcode products' published by Royal Mail. Delivery Point is distinct from Addressed Premise because there may be more than one organisation at an address.

DEM
See Digital Elevation Model.

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.

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