Ordnance Survey – Great Britain's national mapping agency
![Ordnance Survey home page [logo]](/images/gui/logo-os.gif){kind=logo}
| Term | Description |
| 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. |
| Addressed Premise | A permanent or non-permanent building structure with an address being a potential delivery point for Royal Mail®. |
| 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. |
| 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 | A contract set up between the customer and Ordnance Survey for access to data. For OS MasterMap®, the agreement will be defined in terms of an area of interest, a list of themes, a delivery mechanism, a data format and a set of terms and conditions. All data supply, whether part of a Period Licence Service or Pay as You Use Service, is supplied under an agreement. An agreement does not initiate supply of data. This is done through an order. |
| 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. |
| Application Service Provider | A company that offers individuals or enterprises access over the Internet to application programmes (e.g. GIS) and related services that would otherwise have to be located in their own personal or enterprise computers. This may also include access to relevant related data. |
| 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. |
B
| Term | Description |
| 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. |
C
| Term | Description |
| 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. |
D
| Term | Description |
| 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 metres 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. |
| Descriptive Name | A subtype of Name; positioned by a coordinate pair. |
| Descriptive Term | An optional attribute providing further description of a feature e.g. cliff, scrub, standard gauge track. |
| DGPS | See Differential GPS. |
| Differential GPS | A technique for reducing the error in GPS-derived positions by using additional data from a reference GPS receiver at a known position. The most common form of DGPS involves determining the combined effects of navigation message ephemeris and satellite clock errors (including the effects of SA) at a reference station and transmitting pseudorange corrections in real time to a users receiver, which applies the corrections in the process of determining its position. |
| Digital | Data or voltages consisting of discrete steps or levels. Data which is expressed as numbers (digits) in computer readable form is said to be digital. |
| Digital (Map) Archive | Archival map data stored in digital format. |
| 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 Chart of the World | A vector dataset based on 1:1 000 000 scale air navigation charts produced by the United States Defense Mapping Agency. |
| 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 overlayed with other data to create DTM. |
| Digital Identifier | An identifier that is primarily intended to provide unique and unambiguous feature identification for the purposes of exchanging feature based information between computer systems, or associating data within a computer system. |
| Digital Map | A term used by Ordnance Survey to describe a particular tile of digital map data. |
| Digital National Framework™ | A new nationally consistent geographically referenced framework for Great Britain, comprising the National Grid and the National Geographic Database that defines each geographical feature as it exists in the real world with a maintained unique reference allocated to each feature. DNF® is not a product. It is the framework on which Ordnance Survey's future products will be based. |
| Digital Terrain Model | A 3D representation of the Earth's surface. It's construction includes a height model (i.e. a DEM) and overlaid with map data relating to features on the surface (i.e. Map Data or Aerial Photograph). |
| Digitising | Conversion or encoding of existing maps from an analogue form (paper) into digital information, usually in the form of Cartesian coordinates. This may be via a digitising table or tablet with a hand-held cursor, or via a scanner. |
| Dilution of Precision | A dimensionless number that accounts for the contribution of relative satellite geometry to errors in position determination. Generally the wider the spacing between the satellites being tracked by a GPS receiver, the smaller the position error. The most common quantification of DOP is through the position dilution of precision (PDOP) parameter. Other DOPs include the geometric dilution of precision (GDOP), horizontal dilution of precision (HDOP) and vertical dilution of precision (VDOP). |
| DIP | See Document Image Processing. |
| Dirichlet Tesselations | See Thiessen Polygons. |
| Disk Mirroring | A security feature that protects against hard disk failure by copying data from one hard disk to another. The latter operates automatically should the first fail. |
| Distinctive Name | A name given to a feature or place to distinguish it from other features or places of a similar nature e.g. River Thames, Park Lane Methodist Church, Leeds or New Forest. |
| Distributed Component Object Model | The conceptual model which underlies Microsoft's ActiveX technology. The component model describes how components (which may be on different machines) may interact with each other. |
| DNF | See Digital National Framework. |
| DNS | See Domain Name System. |
| Document Image Processing | This involves capturing a digital image of paper-based information using scanners and DIP software. At this stage you can also incorporate OCR software for automatic data capture. |
| Domain (Application Context) | The body of knowledge defining the range and scope of an application in terms of elements, rules and behaviours. More specifically as applied by the Ordnance Surveys a domain is a body of data that shares a common creation and maintenance regime. |
| Domain (System Context) | A class of systems that have similar requirements and capabilities. |
| Domain Name System | Allows the TCP/IP addresses, basically just a series of numbers, to be organised as meaningful addresses e.g. www.ordnancesurvey.co.uk |
| DOP | See Dilution of Precision. |
| Doppler Effect | The shift in the frequency of a received radio signal due to the relative motion of the transmitter and receiver. |
| Dots per Inch | A measurement of input device resolution. |
| Down-Sampling | The reduction in resolution of an image, necessitating a loss in detail. |
| Dpi | See Dots per Inch. |
| DTM | See Digital Terrain Model. |
E
| Term | Description |
| Easement | The right, priviledge or liberty given to a person or group to use land belonging to another for a specific and definite purpose e.g. the right given to an electricity company to bring electricity transmission lines across a private property. |
| Eastings | See Rectangular Coordinates. |
| E-Delivery | The delivery of digital products and services to customers by electronic means, primarily by use of Internet technology. |
| Edge | See Link. |
| The exchange of text messages and computer files over a communications network. | |
| Encryption | Using a set of either public or public/private keys to encrypt and decrypt data, it ensures that information is unreadable by anyone other than the intended recipient. |
| Entity | Something about which data is stored in a databank or database e.g. building or tree. The data may consist of relationships, attributes, positional and shape information and so on. Often synonymous with Feature. |
| Entity Type | A grouping of entities with common characteristics. |
| EOR | See Extent of the Realm. |
| Ephemeris | A description of the path of a celestial body indexed by time (from the Latin word ephemeris meaning diary) The navigation message from each GPS satellite includes a predicted ephemeris for the orbit of that satellite valid for the current hour. The ephemeris is repeated every 30 seconds and is in the form of a set of 16 Keplerian-type parameters with corrections that account for the perturbations to the orbit caused by the earth's gravitational field and other forces. |
| Extensible Mark-up Language | A markup language used on the Internet to describe contents of documents, datasets and other entities. HTML is a subset of XML. |
| Extent of the Realm | The Territorial Waters Jurisdiction Act 1878 and the Territorial Waters Order in Council 1964 confirm that the extent of the realm of Great Britain as used by Ordnance Survey is properly shown to the limit of mean low water (mean low water springs in Scotland) for the time being (except where extended by Parliament). The external bounding lines of Land-Line data is the extent of the realm. |
| Extranets | Company to company intranets that allow access only to authorised users. |
F
| Term | Description |
| Face | A surface bounded by a closed sequence of edges. Faces are contiguous and fill the spatial extent of the dataset and do not overlap. |
| Feature | A digital representation of a real world entity or an abstraction of the real world. It has a spatial domain (attribute), a temporal domain, or a spatial/temporal domain as one of its attributes. Examples of features include almost everything that can be placed in time and space, including desks, buildings, cities, trees, forest stands, ecosystems, delivery vehicles, snow removal routes, oil wells, oil pipelines, oil spill and so on. Features are usually managed in groups as feature collections. In the context of the Ordnance Surveys, a feature may not be mobile. |
| Feature Code | A numeric attribute used in digital map data to describe each feature in terms either of the object surveyed or its representation on the map (or both). A feature code is equivalent to a layer in DXF. |
| Feature Identifier | A unique code to identify an individual feature. |
| Feature Serial Number | A number used as a feature identifier usually allocated on a sequetial basis e.g. The order in which features are digitised. |
| Feature Serving | A service which allows any application (Ordnance Survey, licensed partner or third party) to access the OS MasterMap database direct, online and in real-time. The applications will be able to make data requests and be supplied with the resultant features in GML. It is a purely machine-to-machine service (application to database) and replaces local holdings of data with real-time, online access to a remote holding (i.e. the OS MasterMap database) This service will be made available via a Web feature server. see also Map Serving. |
| Feature Type | A fundamental or primary classification of a feature. Examples are more precise examples building, archway, coniferous tree, benchmark. |
| Field | A specified part of a record containing a unit of data. |
| File | An organised collection of related records. The records on a file may be related by a specific purpose, format or data source and the records may or may not be arranged in sequence. A file may be made up of records, fields, words, bytes, characters or bits. |
| File Set | The set of files required to describe a single data supply in a given format. Where the format enables all the data to be contained in a single file, the file set will be the same as the file. |
| File Transfer Protocol | A protocol which allows a user on one computer to transfer files to and from another computer over a TCP/IP network (e.g. Internet). This will be the method by which OS MasterMap data is made available for online supply. |
| Firewall | Used as a security measure to protect intranets from the traffic that passes in and out of them. A combination of hardware and software that manages authorisation of uses trying to access the intranet. The firewall bars unauthorised data packets from entering or leaving a network. Firewall software specifies which data packets are authorised. It typically resides on routers or dedicated servers. |
| Flatbed Scanner | Any scanning device that incorporates a flat transparent plate on which original images are placed for scanning. The scanning process is linear rather than rotational. |
| Footprint | The ground area occupied by an object e.g. a building. |
| Foreshore | The foreshore is taken to be the area of land between mean high water (MHW) or mean high water springs MHWS) in Scotland and the extent of the realm. |
| Format (1) | The process of "initialising" a floppy disk so that it can be used to store data. |
| Format (2) | The specified arrangement of data e.g. The layout of a printed document, the arrangement of the parts of a computer instruction, the arrangement of data in a record. Different programs store data in different formats. |
| Free End | The end of a line feature which does not intersect or connect with any other line feature i.e. The point defining the free end does not share a coordinate pair with any other feature. Note: It may be coincident with a point feature e.g a post box on the end of a wall. |
| FSN | See Feature Serial Number. |
| FTP | See File Transfer Protocol. |
| Fuzzy Logic | A means of quantifying uncertainty. Allows us to represent statements such as "John is very tall" without having to define hard limits for "tall". Words like "very", "fairly" and "quite" can be represented in mathematics. |
| Fuzzy Search | A search which encompasses words that either look or sound very similar e.g. A fuzzy search for Smith might include Smythe or Smit. |
G
| Term | Description |
| Gazetteer | A list of spatial entities held in computer or printed form, such as properties or streets, which allows for rapid search or query. |
| Geocode | The element in a database used to identify the location of a particular record e.g. a postcode. The process of geocoding is similar to that of address matching in that a data file is compared against a file of geocode and their associated coordinates. |
| Geodata | Information that identifies the geographical location and characteristics of natural or man-made features and boundaries of the earth. Geodata represent abstractions of real world entities such as roads, buildings, vehicles, lakes, forests and countries. |
| Geodemographic Data | Statistical population data, or demographic data, with a spatial reference. For example, census information based upon enumeration districts. This is a type of map data. |
| Geodetic Datum | A set of parameters defining coordinate systems for all or parts of the earth. These datums have been refined and revised over time e.g. NAD 27 is the North American datum for 1927, ED50 is the European datum for 1950 and WGS is the World Geodetic System for 1984. |
| Geographic Information | Information about objects or phenomena that are associated with a location relative to the surface of the earth. A special case of spatial information. |
| Geographical Information System | 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. |
| Geography Mark-up Language | The subject of a recommendation paper from OpenGIS, which describes a markup language based on XML, used to store and transfer geographic data over the Internet (specifically geographic data which conforms to the OpenGIS simple features specification). |
| Geoid | An imaginary shape for the earth defined by mean sea level and its imagined continuation under the continents at the same level of gravitational potential. |
| Geoidal Height | The height of a point on the geoid above on ellipsoidal reference surface. |
| Geometric Data | Data about position within an absolute or relative coordinate system. |
| Geospatial Data | Another term used to describe Map Data but commonly isn't directly associated with a map e.g. An address has a spatial reference associated with it but not in map coordinates. |
| GI | See Geographic Information. |
| GIS | See Geographical Information System. |
| Global Positioning System | A system of coordinating a ground position in three dimensions using radio transmissions from a pattern of US defence satellites. |
| GML | See Geography Mark-up Language. |
| GPS | See Global Positioning System. |
| Graphical User Interface | A method of interaction with a computer which uses pictorial buttons (icons) and command lists controlled by a mouse. It is generally regarded as simpler and easier to learn than command line interfaces, where commands have to be typed. Examples include MS WINDOWS for PCs, Open Look or MOTIF for workstations and System 7 for Macintosh. |
| Greyscale | A continuous tone image comprising black, white and grey data only. |
| Grid | The planimetric frame of reference e.g. The National Grid. |
| Grid Goordinates | A plane-rectangular coordinate system based on and mathematically adjusted to a map projection in order that geographic positions (latitudes and longitudes) may be readily transformed into plane coordinates and the computations relating to them made by the ordinary methods of plane surveying. |
| Ground Height | The height where the building wall intersects the ground. |
| Ground Station | A facility capable of receiving signals from earth observation satellites such as LANDSAT, SPOT, ERS, JERS AND MOS. |
| GUI | See Graphical User Interface. |
H
| Term | Description |
| Hard Disk | A device containing one or more inflexible disks coated with material in which data can be recorded magnetically, together with their read/write heads, head positioning mechanism and the spindle motor in a sealed case. This offers high capacity data storage. Most hard disks are permanently sited in a computer. |
| History | A record of change over time for features or objects e.g. a boundary change. In the context of geospatial data, the storage (and potentially the supply) of deleted features and superseded versions of features. |
| Holdings | See Agreement. |
| Home Page | The first page of a Web site, whether on Internet or an intranet. |
| HTML | See HyperText Markup Language. |
| HTTP | See HyperText Transfer Protocol. |
| Hydrographic Surveying | The measurement and description of the physical features offshore and adjoining coastal areas with special reference to their use for the purpose of navigation. |
| Hypertext Link | These allow the user to jump from one page/Web site/document to another by generating a browser request simply by clicking on the link. These links are often depicted in blue, underlined text. |
| HyperText Markup Language | An open format for sharing electronic text documents with hypertext extensions via the Internet/Intranet. |
| HyperText Transfer Protocol | The simple request/response protocol that runs on top of TCP/IP that allows Web browsers to access files on any Web server. |
I
| Term | Description |
| Identifier | A form of identifying or labelling a feature. An identifier need not be unique or unambiguous. Types of identifier are address, text label and digital identifier. |
| Independent Polygon | One of the options for OS MasterMap product feature geometry/topology in which the data is simplified into area, point and line features with no relationship between them and with their own explicit geometry. For example, in the Independent Polygon product, the bounding line between two areas will be represented three times, each with its own description of the geometry: once as a line feature, once as part of the bounding line of the first area feature and once as the bounding line of the second area feature. |
| Inferred Links | Line features representing inferences about the real world, rather than topographic statements of fact. These sensibly subdivide certain types of area feature where there is no appropriate topographic detail. They are normally used to: divide road sections, separate individual garden plots in residential areas where no dividing fence, wall or hedge exists, close junctions btween roads and car parks or hard standing areas, close fields which have simple breaks in the hedge or wall rather than gates. These will be automatically created using software and initially OS expects to be able to create polygons for around 95% of urban areas using this method. Inferred links sensibly subdivide certain types of area feature where there is no appropriate topographic detail. Quality will be variable initially, but we are investigating methods of improving this information. |
| Integrated Services Digital Network | A telecommunications standard which enables the transmission of voice data and certain images over telephone lines through end-to-end digital circuits. |
| International Standards Organisation | An organisation established to promote the development of standards to facilitate the international exchange of goods and services and to develop mutual cooperation in areas of intellectual, scientific , technological and economic activity. |
| Internet | The combined collection of interconnected global computer networks that use TCP/IP protocols and are public domain i.e potentially available to all. |
| Internet Service Provider | Organisations that offer commercial connection to the Internet network. |
| Interoperability | See OpenGIS. |
| Interpolation | The estimation of values of a surface at an unsampled point based on the known values of surrounding points. |
| Intranet | A private network that uses Internet standards and protocols but enables full control within an organisation for the provision of corporate information and services to employees. |
| ISDN | See Integrated Services Digital Network. |
| ISO | See International Standards Organisation. |
| Isoline | A line joining points of equal value. Examples of these include height contours on a map or isobars showing atmospheric pressure on a weather map. |
| ISP | See Internet Service Provider. |
J
| Term | Description |
| Java® | A full object-oriented programming language developed by Sun Microsystems. Java is architecturally neutral and portable in that it can support applications operating across a wide variety of operating systems. |
| JavaBeans | A component model for the Java programming language. Components written in Java can be "plugged together" using the JavaBeans protocols. |
| JavaScript | An object-based language which enables non-programmers to create applications similar to Java. It supports only some of the functionality of Java in an effort to overcome some of its complex features. |
| Joint Photographic Experts Group | An organisation that has defined various file compression techniques. The most common graphics format on the Internet. |
| JPEG | See Joint Photographic Experts Group. |
L
| Term | Description |
| Land Information System | A system for capturing, storing, checking, integrating, manipulating, analysing and displaying data about land and its use, ownership and development. |
| Land Parcel | An area of land, usually bounded by real world features or implied alignments and usually with some implication for land ownership or land use. |
| Land Terrier | Traditionally a document system comprising a set of marked maps and ledgers containing textual information to record land and property - can be emulated by many GISs. |
| Large-Scale | The term used to refer to a map or map data that concentrates on small areas. It is called large scale because the features that appear on the map will look larger than those at a small scale. For example a building may appear as its outline (or footprint). |
| Laser Induced Direction and Range | Airborne laser scanning system which accurately measures DEMs. May be used for flood monitoring and prediction, building detection and building heighting, tree height measurement and general DEM production. |
| Latitude | The angular distance north or south between a point on the earth's surface and the equator. The distance is measured with reference to an idealised spheroid shape of the earth. |
| Layer | Equivalent to Theme. |
| Licensed Partner | Any organisation that has entered into a formal licence agreement with OS to market map information or to incorporate map data with their application or service. A Licensed Partner may also be a customer in their own right. |
| LIDAR | See Laser Induced Direction And Range. |
| Line | A series of connected coordinated points forming a simple feature with homogeneous attribution. |
| Line Feature | The spatial abstraction of an object in one dimension. Lines may intersect with other lines. They are defined as a series of two or more coordinate pairs and may be curved or straight. Curved lines consist of a series of very short straight line segments. Lines may be concurrent with other lines under certain conditions. As an object abstraction a line has no width. |
| Line Segment | A vector connecting two coordinate points. |
| Link or Edge | Links are the representation of line features. They are made up of one or more consecutive non-intersecting link segments with common attributes between two terminating nodes. Links have no connection with other links except at the start or end, via common (shared) terminating nodes (points). Al links contain their terminating coordinates. Links may form the boundaries of polygons and may be shared between polygons. |
| Link-Node Topology | A data structure used to represent connectivity between line features. Link-node topology supports the definition of linear feature and polygon boundaries and supports analysis functions such as network tracing. |
| LIS | See Land Information System. |
| Local Holdings | The situation where a customer has to hold and manage data which is supplied to them. |
| Logical Record | A logical record contains all the information relating to a data entity e.g. a feature record. A logical record may comprise one or more physical records. |
| Longitude | The angular distance of a point east or west of an arbitrarily defined meridian, usually taken to be the Greenwich meridian. The distance is measured with reference to an idealised shape of the earth. |
M
| Term | Description |
| Map Data | Digital data that has a spatial component. Typically these are digital maps but can also include data that has some form of spatial attribute that can be linked to a real world location - i.e an address. |
| Mean High Water/Springs | Depiction of the encroachment of land by tidal waters at mean highest levels - spring tides in Scotland. |
| Mean Low Water/Springs | Depiction of the limits of tidal waters at mean lowest ebb - spring tides in Scotland. |
| Metadata | Graphical or textual information about the content, quality, condition, origins and characteristics of data. |
| MHW or MHWS | See Mean High Water/Springs. |
| MLW or MLWS | See Mean Low Water/Springs. |
| Modelling | The process of creating a representation of part of the real world and subjecting it to some form of parameters and variables for the purpose of predicting, simulating or describing the real world. |
N
| Term | Description |
| Name or Text Feature | The proper name or label of an object (real world) or feature (object abstraction) consisting of one or more text strings. A name position is defined by a coordinate pair. |
| National Geospatial Data Framework | A UK initiative involving various public and private sector organisations involved in GIS and Map Data who want to create the infrastructure to make disparate data sets easily accessible. |
| National GPS Network | The infrastructure of active and passive GPS reference stations which allow surveyors to determine precise coordinates in GPS and British National Grid spatial reference systems. The National GPS Network provides the physical definition of the British National Grid, the primary spatial reference system used in the OS MasterMap. A central component of the OS MasterMap. |
| National Grid | A metric grid based on the Tranverse Mercator Projection developed by Ordnance Survey in 1936 for use in Great Britain. Referred to in GIS by the code "OSGB36®" it is the de facto standard projection for display of UK based mapping. |
| National Land and Property Gazetteer | A spatial database of indexed records relating to land and property ownership. Technically this is a Terrier rather than a Cadastre. |
| National Land Information System | A conveyancy service designed to make the legal processes associated with buying a property more efficient. It combines land and property data with local authority information to cover the legally recuired local land search coving land charges and inform. |
| National Land Use Database | A database of land use. Currently contains information on brown field sites supplied by Local Authorities but will in the future cover the entire country and different land cover. |
| Neatline | The outer grid lines, forming the boundary of the map sheet. |
| Network | A model representing the interconnected elements through which some form of resource can be transmitted or will flow. |
| Newsgroups | Similar to Bulletin Boards except that the reader membership can be controlled. These are often used by more specialised groups for exchange of information where a common interest is held andcan vary in size depending on the size of audience intended. |
| NG | See National Grid. |
| NGDF | See National Geospatial Data Framework. |
| NLIS | See National Land Information System. |
| NLPG | See National Land and Property Gazetteer. |
| NLUD | See National Land Use Database. |
| Node | An object representation of a point which either does not form any part of a link (isolated node or polygon seed point; or is the representation of a point at the start or end of a link (terminating node). The position of a node is represented by a single coordunate pair; which is repeated within all links logically connected at that node and/or containing it. |
| Noise | In a scanning context this refers to random, incorrectly-read pixel values, normally die to electrical interference or device instability. |
| Northings | See Rectangular Coordinates. |
O
| Term | Description |
| Object | Object when referring to a geographic feature will not be used. Feature is the preferred term. |
| Object Database | Stores software objects rather than rows of data in tables. |
| Object Database Management Systems | The software which manages and controls an object database. |
| Object Orientation | A data model that treats components of a program or database as individual entities. These 'objects' encapsulate knowledge about how the entity responds and reacts to the system and inherits functionality from generic classes of objects. |
| Object-Based Data | Data inwhich one entity (i.e. One feature) represents one real world object (e.g. A building or land parcel). |
| ODBMS | See Object Database Management Systems. |
| Office for National Statistics | UK government agency. |
| Off-Line Supply | The supply off data to a customer on physical media (e.g. CD, DVD). |
| OGC | See Open GIS Consortium. |
| OGIS | Open Geodata Interoperability Specification. |
| Online | A computing device or program that is activated and ready for operation is said to be online. |
| Online Supply | The supply of data to a customer using Internet technologies. |
| ONS | See Office for National Statistics. |
| OO | See Object Orientation. |
| Open GIS Consortium | A consortium of vendors, producers and users of geospatial data dedicated to defining the standards to allow different GIS software components to internally exchange GI and requests and thus work seamlessly. This functionality is called interoperability. |
| Orbital Perturbation | The deviation of an orbit from some orbit taken as standard; in particular the deviation from a Keplerian orbit. |
| Ordnance Datum | The mean sea level at Newlyn in Cornwall calculated between 1915 and 1921, taken as a reference point for the height data on Ordnance Survey maps. |
| Ordnance Survey of Ireland | National mapping agency of Ireland. |
| Ordnance Survey of Northern Ireland | National mapping agency of Northern Ireland. |
| Orientation | Orientation of a point or a text feature measured in degrees anticlockwise from grid east. |
| Origin | The zero point in a system of rectangular Cartesian coordinates. |
| Orthogonal | At right angles to each other. |
| Orthoimage | See Orthophoto. |
| Orthophoto | Photographic image, rectified to remove the distortions caused by variations in terrain height, resulting in an image in which all pixels are to the same scale. |
| OSI | see Ordnance Survey of Ireland. |
| OSNI | See Ordnance Survey of Northern Ireland. |
| Overhaul | The process of refashioning the old County Series 1:2500 scale maps to adequate National Grid standards. It included the adjustment of the detail on the old maps to the control points of the 1936 retriangulation, the recompilation of the maps on the national Transverse Mercator Projection and with sheet lines corresponding to the National Grid., the elimination of errors (particularly those caused by distortion of materials and inadequacy of old revision methods), the revision of detail and finally, the fair drawing of all maps to a new specification. Early experiments were carried out in the Cotswolds and therefore the method is often referred to as the Cotswold Adjustment. Overhaul was carried out between 1948 and 1980. |
P
| Term | Description |
| PAF | See Postal Address File. |
| Paradigm | A set of assumptions, concepts, values and practices that constitutes a way of viwing reality for the community that shares them, especially in an intellectual discipline. |
| Parallel | A line of latitude. |
| Parameter | A quantity that is fixed for the case in question, but may vary in other cases. |
| Parcel | See Land Parcel. |
| Pay as You Use | A service provided by Licensed Partners giving access to Ordnance Survey data for business use on a transaction basis with or without added value services. The transactions available will be defined as View, Plot, Data Export and Analysis. The transaction will not include any update maintenance provision. Each access to the data will incur a data charge related to the type of transaction. In the case of data export, the data will include a business licence for a period of 12 months only. |
| PAYU | See Pay as You Use. |
| Period Licence | A licence to use a data product or any other value added service or product derived from detailed datasets for business use for an agreed period of one or more years. It covers the initial supply of the data and supply of update. |
| Perl | A scripting language popular for writing CGI applications due to its ability to create powerful data and text manipulation programs. |
| Perturbation | See Orbital Perturbation. |
| Photogrammetry | The science, art and technology of obtaining reliable measurements and maps from aerial photographs. |
| Pixel | A picture element of a raster image as displayed on a screen or raster plot. |
| Platform Independent | A term usually applied to a piece of software that can operate on many different hardware platforms e.g. PC, Unix, Mac, VAX etc. |
| Plot | The provision of an extract of the data as a single plot or print on paper or similar medium. |
| Point | A zero-dimensional spatial abstraction of an object represented by a coordinate pair. |
| Point and Line Data Structure. | A form of vector data structure designed for map production in which all map features are designated as points or lines or text. Point and line data does not carry the topological relationships between features. |
| Point Feature | A zero-dimensional spatial abstraction of an object with its position defined by a coordinate pair. Points may also be represented by symbols which may have attributes such as orientation and size. |
| Polygon | Polygons are representations of areas. A polygon is defined as a closed line or perimter which completely encloses a contiguous space and is made up of one or more links. At least one node occurs on the perimeter of a polygon where the bounding link completes the enclosure of the area. There may be many nodes connecting the bounding links of a polygon. Links may be shared between polygons. Polygons ma wholly contain other polygons; or be contained within other polygons. |
| Polygon Boundary | The link or links which enclose a polygon, projected into the horizontal plane. |
| Polygon Point | See Representative Point. |
| Polyline | A line made up of a sequence of line segments. |
| Portal | A web-site or service that offers a window into a broad array of resources and services. A portal also allows the provider and/or user to customise the content of the web-site to meet individual needs. |
| 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 coordinates system is based. |
| Positional Quality | Gives an indication of the positional accuracy of the location coordinates in ADDRESS-POINT. |
| Postal Address | A series of instructions used by Royal Mail to sort and distribute mail to a delivery office for delivery to the intended recipient. It contains only those address elements that are necessary to identify one delivery point from another to assist Royal Mail in the delivery of mail. There may be many delivery points within an individual building structure as shown in Land-Line data. |
| Postal Address File | Created when all the sparately held information was assembled and stored on a Royal Mail central computer system. PAF® now contains the postal addresses and postcodes of approximately 25 million delivery points including approximately 170 000 large users. |
| Postcode | The units by which the delivery of post is managed by Royal Mail. There are four components to the code: The "Area", i.e. "SO", the "District", i.e. "16", the "Sector", i.e. "4" and "Unit", i.e. "GU". A so-called "Unit Postcode", the smallest postal unit. |
| Pre-Build | Depiction of detail before construction. |
| Protocol | A formally agreed standard for communication between computers. |
| Proxy Server | A server that acts as an intermediary between a client and the server the client wants to access. It is the proxy server that makes the request to the server of interest and passes back the response to the client. |
Q
| Term | Description |
| Query | The process of selecting features in a database. Can be acheived through a query language directly on the data or, in a GIS, by interactively selecting features. |
R
| Term | Description |
| RAD | See Rapid Application Development. |
| Rapid Application Development | An approach to software development based on close collaboration with users and a continuous iterative delivery of software. |
| Rasterisation | The process that converts vector data, which is a series of points, lines and polygons into raster data which is a series of cells with a discrete value. |
| RDBMS | See Relational Database Management System. |
| Receiver Independent Exchange | Exchange format for GPS observations. Provision is made for pseudorange, carrier phase and Doppler observations. |
| Record | A set of related data fields grouped for processing. |
| Rectangular Coordinates | Also known as x-y coordinates and as eastings and northings. These are two-dimensional coordinates which measure the position of any point relative to an arbitrary origin on a plane surface e.g. A map projection, a digitising table or a VDU screen. |
| Red, Green and Blue | The primary colours of light perceived by the eye. |
| Reformed Mapping | A method of improving the accuracy of overhaul mapping. It consists of a partial resurvey based on air triangulation and completion by fit and trace methods of pockets old detail to match the new. |
| Relational Database | One which stores data in rows and tables e.g. Oracle, MS Access. |
| Relational Database Management System | The software which manages access to a relational database. |
| Relative Accuracy | Relative accuracy compares the distance between features measured on the ground to the corresponding information contained in the map data. When measuring between data points represented on the map it is worth noting that some distortion may occur due to the materials and process used to produce the map. |
| Relative Coordinates | A coordinate pair or triplet measured relative to another point in the coordinate system in which it lies, rather than from the origin. (see also absolute coordinates). |
| Remote Holdings | The situation where the supplier holds and manages the customer's data. |
| Remote Sensing | The process of obtaining information about an object whilst separated by some distance from the subject. Practically, this is a term used to describe the process of using sensors mounted on satellites to observe the Earth's geology, surface and atmosphere. |
| Representative Point | A point within a polygon that can be used to carry the attributes of the whole polygon e.g. owner or land use type. Also called area seed, peg point, point label, polygon point, polygon seed. Representative points are not included in OS MasterMap data. |
| Resampling | An increase or reduction in the number of pixels in an image, reqired to change its resolution without altering its size. See also down-sampling and interpolation. |
| Resolution | A measure of the ability to detect quantities. High resolution implies a high degree of discrimination but has no implication as to accuracy e.g. In a collection of data in which the coordinates are rounded to the nearest metre, resolution will be 1 metre, but the accuracy may be +/-5 metres or worse. |
| Resurvey | The complete survey of detail based directly on National Grid control (OSGB36). It may be completed wholly on the ground or by a combination of aerial and ground survey methods. |
| RGB | See Red, Green and Blue. |
| RINEX | See Receiver Independent Exchange. |
| Road Centreline | An implied and imaginary line depicting the centre of a road carriageway (represented by FC0098 in Land-Line in NTF or G8010098 in Land-Line in DXF). They are not specifically surveyed or precisely positioned within the data. They are digitised to fall between curb lines, but will nit necessarily fall equidistantly between them. |
| Rotation | Movement of a vector through an angle. |
| Router | In a message switching system, the portion of a node or exchange that examines incoming messages, interprets the address information and determines which of the outgoing links can be used. Usually a computer program that chooses messages from incoming buffers and places them into outgoing message queues. |
| RS | See Remote Sensing. |
| Rubber Sheeting | A process which adjusts the relative positions of features within a dataset in a non-linear or non-uniform way. It is used to transform the coordinates of maps with different scales, orientation or coordinate systems. |
S
| Term | Description |
| Sampling | The process of converting analogue data into digital data by taking a series of samples or readings at equal time intervals. |
| Scanning | Capturing an image using an optical input device that uses light sensing equipment. The image is translated into a digital signal that can be manipulated by optical character recognition software or graphics software. |
| Schema | A description of a feature's attributes or, more specifically, the specific attribution model for a feature in terms of primitive data types and constraints on these types. |
| Segment | A link or line defined by two consecutive coordinates in a line string. |
| Server | A program that runs on a networked computer that responds to client programs running on other networked computers. |
| Service Level Agreement | See Collective Agreement. |
| Shapefiles | A simplistic geospatial data structure in which objects are stored individually with no explicit information about the relationships between those objects. |
| Single Precision | Refers to a level of coordinate accuracy based on the number of significant digits that can be stored for each coordinate. Single-precision numbers store up to 7 significant digits for each coordinate. |
| SLA | See Service Level Agreement. |
| Small Scale | The opposite of large scale and relates to a map that covers a wide area. Called small scale because features that appear on the map will look to be smaller in size than those on a larger scale map. |
| Snapping | An operation or process whereby whereby the computer will move a point or line slightly so that it corresponds to a nearby point or closest point on a nearby line. |
| Soft Clipping | All line features that fall across a query area are supplied complete. For areas, the area feature itself will refer to all the lines that bound it. However, only those lines partly or entirely within the query area are supplied. OS MasterMap data will only be supplied unclipped. |
| Spaghetti Data | Vector data composed of line segments which are not topologically structured or organised into objects and which may not even be geometrically clean. Spaghetti data can be useful however if all that is required is a visual image or a plot of a map. |
| Spatial Analysis | A family of analytical techniques associated with the study of spatial objects, their location, geometry and attributes. The analysis can simply be visual, by association and location, or mathematical. |
| Spatial Data | Another term used to describe Geospatial Data. |
| Spatial Entity | See Feature. |
| Spatial Query | The process of selecting features based on location or spatial relationship e.g. Select all features within 300 metres of a road. |
| Specification | Technical description of the structure and schema associated with a specific dataset or product. |
| Spheroid | A surface generated by revolving an ellipse about one of its axes. Specifically used for a surface whose dimensions are chosen to approximate to the shape of the earth. |
| Spline | A term meaning a type of polyline created not by coordinate pairs but by anchors that influence the bearing of the line. A beizier curve and Bline are other examples. |
| Spot Height | A point on the earth's surface for which the height above a reference datum is known and which has been fixed by observation. |
| SQL | See Structured Query Language. |
| String (1) | A set of items which can be arranged into a sequence according to a rule. See also Character String. |
| String (2) | A sequence of coordinate pairs or triplets making up a line or link. |
| Structured Data | Data within which collections of features (of any type) form objects. |
| Structured Query Language | An international standard language for manipulating and interrogating relational databases. It is commonly used in querying spatial attributes in GIS. For example "Select * from Map where value > 203". It can also be extended to include spatial operations. |
| Supply Format | The file format in which the data is supplied to the customer. OS MasterMap data is only being supplied in GML. |
| Surveying | The determination of the absolute and relative positions of points, on or near the earth's surface , by means of measurement in the three elements of space; distance, direction and elevation, and hence their subsequent representation onto a plane surface, exhibiting them in their correct horizontal and vertical relationships. |
| Symbol | A graphic representation of a concept that has meaning in a specific context. |
| Symbol Feature | A feature represented by a graphical sign with a specific meaning e.g. triangulation pillar or bench mark. |
T
| Term | Description |
| Table | A representation of data in a database. It is organised into records (rows or tuples) and attributes (columns). The attributes for map data, such as area, number of residents for example will be stored in tables. |
| Tagged Image File Format | A popular image file format for storing scanned images. It is supported by the majority of image-editing programs running on a variety of computer platforms. |
| TCP/IP | See Transmission Control Protocol / Internet Protocol. |
| Terrier | See Land Terrier. |
| Text Attributes | A series of parameters defining the characteristics of the text displayed on a map. Text attributes include colour, font, size, location and angle. |
| Text String | The set of characters to be plotted as a text feature; it is indivisible in the data. |
| Textual Fidelity | The correctness of text within a geographic dataset. |
| Thematic | Depicting one or more specific topics or subjects e.g. Land use, rainfall, population density. |
| Thiessen Polygons | A method used to divide an area into polygons so that all locations closest to a particular sample point are enclosed within a single polygon. The boundary lines are defined at positions equidistant between two adjacent points. Also known as Dirichlet tesselations and Voronoi polygons. |
| TIFF | See Tagged Image File Format. |
| TIGER | See Topologically Integrated Geocoding and Referencing. |
| TOID | See Topographic Identifier. |
| Topographic Database | A database in which data relating to the physical features and boundaries on the earth's surface is held. |
| Topographic Identifier | A 16 digit number that uniquely identifies every feature. No intelligence (e.g. Its coordinate position) about the feature can be derived from either the allocated number or the process by which it is allocated. The TOID will remain with the feature throughout its life and will not be reassigned to a new feature when the existing feature is deleted. |
| Topographic Map | A map for the principle purpose of portraying and identifying the features of the earth. |
| Topography | The study of the physical features of the earth. |
| Topologically Integrated Geocoding and Referencing | A data format developed by the US Bureau of Census for the 1990 US census. |
| Topology | Properties of geometric forms that remain invariant when the forms are deformed or transformed by bending, stretching or shrinking. Among the topological properties of concern in GIS are connectivity, order and neighbourhood. |
| Transfer Format | The format used to transfer data consistently between computer systems. In general usage this can refer not only to the organisation of data, but also to the associated information, such as attribute codes which are required in orderto successfully complete the transfer. |
| Transfer Medium | The physical medium on which digital data is transferred from one computer system to another e.g. CD-ROM. |
| Transmission Control Protocol / Internet Protocol | The common communication protocol of the Internet. Each computer connected to the Internet has a TCP/IP address which identifies it. Other protocols such as HTTP are built on top of TCP/IP. |
| Triangulation Station | A permanently marked and fully documented control station whose position on the earth's surface has been established to a high accuracy both absolutely and in relative terms to other adjacent stations by means of angular or electronic distance measrement. Triangulation stations form the framework on which all survey and mapping techniques are based. |
| Tuple | A set of n coordinates representing a point in n-dimensional space, as defined by a spatial reference system. The British National Grid reference system is 2D only, so coordinate tuples consist of an easting and a northing coordinate. |
U
| Term | Description |
| UKSGB | See United Kingdom Standard Geographic Base. |
| UML | See Unified Modelling Language. |
| Unclipped (Data Supply) | All feature which lie wholly or partly within the query area are supplied and the full geometry of each of these features will be included in the supply. OS MasterMap data will only be supplied unclipped. |
| Unified Modelling Language | An OO notation for expressing anslysis and design. The notation is a collaboration between the athors of the three most populat OO methods and is becoming a de-facto standard among the OO development community. UML is an OMG standard. |
| Uniform Resource Locator | The way that the protocol, server, address and path are addressed to uniquely identify Internet resources. |
| United Kingdom Standard Geographic Base | The means of identifying a standardised core of commonly used geographic units, a definite source of data about these core units and the existing datasets that support these units. |
| URE | User Range Error. |
V
| Term | Description |
| Vector | A straight line joining two data points. |
| Vector Data | Positional data in the form of coordinates of the ends of line segments, points, text positions and so on. |
| Vertex | An intermediate point in a polyline. |
| Virtual Private Network | A set of nodes on a public network such as the Internet that communicate among themselves using encryption technology to protect their messages from being intercepted and understood by unauthorised users. |
| Voronoi Polygons | See Thiessen Polygons. |
| VPN | See Virtual Private Network. |
W
| Term | Description |
| Web Site | A group of related HTML documents and associated files, scripts and databases that is served up by an HTTP server on the World Wide Web. |
| Webmaster | A person within an organisation who is responsible for day-to-day technical and editorial maintenance to the Web site. |
| Word | A group of characters representing a unit of data and occupying one storage location. A word is usually long enough to contain one computer instruction or one integer e.g. 16 or 32 bits. |
| Workflow Application | A software technology that can be programmed to automate the steps in a work procedure, prompting users to carry out jobs and enabling managers to follow work processes and spot bottle-necks. More dynamic workflow software is also available to help groups of people work together on more ad hoc projects. |
| World Wide Web | Public network of Web sites available on the Internet on a global basis, available to any user anywhere in the world. |
| WWW | See World Wide Web. |
X
| Term | Description |
| XML | See Extensible Mark-up Language. |
Z
| Term | Description |
| Zoom | To increase or decrease the scale of the map view window. Zoom out to view a smaller scale map and zoom in to view at a larger scale. |